Glitches

List of glitches and tricks, and information about them.

Physics Glitches
If Mario becomes surrounded by blocks and touches the ground, he will be crushed and die. However, avoiding touching the ground can be done in a number of ways, such as by flying before Mario gets surrounded, or swimming upwards. Video
If Mario is far enough inside a solid tile, he will be pushed leftward by it. Oddly, Layer 2 does will not do this, and instead Mario will be able to freely walk around (though unable to jump).
If Mario is big and stands up or jumps in a one-tile space, he may be pushed through the floor. Also works if Mario lands on Yoshi, and can even occur while Mario is small if he gets stuck in a turnblock during the jump.
Smashola: Doing the above through turnblocks while caped and spinjumping may cause Mario to "warp" his way downward very quickly.
Walljump: With enough speed, Mario can land on the corners of blocks for a frame - even if they're part of a wall - and jump off of it. As an alternative, this frame can also be used to enter doors or pipes, even if they don't normally have ground. More info - Video - Fix
Mario can enter a pipe even if his head is the only part touching it.
Slope clip: Mario can pass through the corners of slope tiles so long as he is moving upward as he crosses it. More info - Video - Fix
Clipping into an upside-down slope will force Mario on top of it. This can also force him inside blocks, killing him.
Clipping into the bottom corner of a block that is on a ledge may cause Mario to be forced on top of the ledge, killing him inside the block.
If Mario hits the vertical screen barrier while walking up a slope, he will fall through the slope.
Corner clip: With enough speed, Mario can "enter" the corner of a block in order to pass through it. If he's small or ducking, though, he may be crushed. More info
If Mario is big, you can also force him into inner corners where a leftside wall and ceiling meet. If the corner is non-solid, he can go through without dying.
Sprite clip: Mario can jump through the corners of some sprites if he hits it at the right angle. Won't do much good if the inside of the sprite hurts him as well, though.
If Mario is ducking when he enters certain states (climbing, balloon), then he will still retain his reduced hitbox size, despite what the graphics for these states suggest. He'll also still be ducking once he exits those states.
If Mario grows from a powerup while in certain phases (climbing, Lakitu cloud) and his head ends up inside a ceiling, he'll be pushed leftward, even through solid blocks.
If Mario has 99 lives and he gets a life through any means, his life counter will briefly increase past 99 for a frame. Exiting a level on that frame (via start+select or a screen side exit) will then display a glitched value for his life counter on the overworld. Entering a new level will fix it, however.
If vertical scrolling is enabled in a level, you can prevent the screen from scrolling by jumping off of the ground the frame that Mario lands on it.
While being "stuck" by a noteblock, Mario can enter solid blocks, though he'll be crushed. Fix
Mario can stick to a row of noteblocks without bouncing off of them if he runs across them at the right speed.
If Mario is moving fast enough (x-speed of 64-80), then Mario will be unable to jump. Any faster and his jump height will also be significantly higher than usual.
Mario can spinjump off of noteblocks if you press A on the frame that he actually bounces off.
The top tile of tileset-specific lava can be used to push Mario into blocks. Interestingly, if Mario is big, it can also be used send him all the way through solid walls or solid floors without being crushed.
The left and right edges of tileset-specific lava are solid.
Mario can swim in standard object lava so long as he doesn't swim too far into the top of the tile.
Mario's P-meter will not decrease while in water.
Layer 2 will not reset Mario's Y speed when he stands on it; this means, if you walk off of a Layer 2 platform, Mario will start falling much faster than he normally would.
When scrolling the screen, Mario will not interact with solid blocks; this can be used to pass through solid Layer 2 blocks if the horizontal scroll setting for them is set to something other than constant.
Mario can survive a few blocks under the bottom of levels.
Changing between powerups while Mario is offscreen will cause his transformation animation to be skipped. Fix
Net punching while climbing can kill sprites other than the Climbing Net Koopas; the only requirement is that Mario and the sprite be on opposite sides of the fence, even if the sprite isn't actually "climbing" it.
Net punching will destroy extended sprites regardless of what side of the fence they're on.
When Layer 2 or Layer 3 is scrolling and has interaction, the relative Layer 2 position ($7E0026) gets added to capespins to handle interaction with between them. Normally, this resets back to Mario when it goes back to handle sprites and Layer 1, but if the game is frozen (via $9D), this doesn't happen, and the relative position keeps gets added repeatedly. This causes the cape hitbox to then fly off along the axis of Layer 2/3's movement during the freeze, hitting any blocks or sprites along the way. More information
Mario can turn while flying by pressing X or Y to capespin.
Fast diving: Mario's flying "frame" will increase or decrease every time a direction is tapped, allowing his speed to increase faster than simply holding it down. With this in mind, you can rapidly press one direction to dive quickly or build big air faster.
Air cancel: You can cancel an air catch through a number of ways, including spinning around, hitting a ceiling, or reversing your speed. If you manage to do this, it can be used to decrease the height given by an air catch (useful for tight passages), or it can be used to catch air while maintaining big air.
Infinite air catch: Based off the above, you can catch big air with a low X speed, use <+B to slow Mario down, and then reverse his speed to cancel the catch. This will give him a significant Y-speed boost while maintaining big air, which can then be repeated an infinite number of times. More info
Mario can "stick" to ceilings if he catches air close enough to it. Simple hold the opposite direction to Mario's direction and he won't start to fall downward. Big air can also be maintained through this glitch.
Mario can regain flight after letting go of X or Y by pressing it again while he is moving downward and his takeoff meter (7E149F) is greater than 2.
If Mario is flying and takes a screen exit, he can regain flight in the next room in the same was described above.
Mario will not lose flight while climbing, nor after collecting a P-balloon, so long as he doesn't touch the ground. It should be noted that, in either case, Mario retains the extra hit from flight even while in that state.
Pressing both left and right at the same time while flying will act as if Mario is pressing just left, but will not affect his X speed.
L+R glitch: Holding down both the left and right directions at the same time while Mario has either a P-balloon or Lakitu cloud will boost Mario rightward at higher speeds than normal, even allowing him to force his way through solid objects without dying. Fix
The timer for the P-balloon continues to decrement even while the game is frozen with $9D.
The item in the item box can be released even while the game is frozen with $9D.
Shooting a fireball at a moving conveyor belt or rope slope will warp the fireball five blocks upward if the slope is moving downward, and ten blocks upward if it is moving upward. The opposite height changes will occur if the fireball hits the slope while moving downward in parallel with it.
Fireballs can pass through the corners formed by two diagonally placed blocks.
Fireballs and silver P-switches can't kill sprites in slot #A or #B.
Mario can kill many sprites that would normally be unkillable by sliding into them, often resulting in a glitched death sprite. You can also get some glitched sprites with star power as well.
Grabbing a vine/fence or collecting a P-balloon while in the sliding state will cause the state to persist, meaning any sprites you touch will be instantly killed. The effect will end if you move horizontally in midair while not holding onto the fence. Video
Killing a sprite by sliding into it will set the counter for the number of sprites Mario has killed with a star to 1. Fix
While the star power timer normally decrements once every four frames, freezing the game (via $9D) on a frame the timer is meant to decrement will cause it to decrease every frame while the game is paused.
The star's kill counter only resets if you come in contact with a sprite that uses default interaction while Mario doesn't have star power. This means you can start building the counter with one star, let it run out, then grab a second star to continue building the counter. Fix
Mario may be killed if he spinjumps on two sprites at the same time. Fix
Destroying a sprite via spinjump will stop Mario's vertical movement, making it possible to reduce jump height to as little as a few pixels.
If Mario is big, ducking on the frame just before he turns upright after wall-running will cause him to clip into the wall.
Mario can survive being crushed by the Layer 3 smashers by alternating A and B every frame.
Mario will "stick" to the bottom of the Layer 3 smashers, making him fall slower if he touches them as they're poking out of the ceiling.
Mario can fly through Layer 3 smashers if he either dives into them at the right angle or gets pushed into them.
Useless
Screen-scrolling while the Yoshi's House smoke sprite is onscreen will cause it to glitch out.
Alternating directions every other frame while swimming with an item will cause Mario to appear as if he's holding the item on his back.
Touching a damaging object (e.g. muncher, spike) while swimming upward will glitch Mario's shrinking animation. Fix
Capespinning or shooting a fireball while running up a wall will cause Mario to stop animating briefly. The abilities will also still behave as if he were horizontal.
If Mario finishes a capespin during the goal walk, the cape's hitbox will persist even after the spin at whatever position he stopped at.

Yoshi-Related Glitches
After mounting Yoshi, Mario can not be hit by enemies for a few frames. Only works with certain sprites, however. More info
Keys and P-switches can still hit blocks while stuck to Yoshi's tongue.
Shells, throwblocks, and Goombas can still hit other sprites while stuck to Yoshi's tongue, so long as the sprite it's hitting is in a lower slot.
Spinjumping onto Yoshi will allow Mario to break turnblocks as if he is still spinjumping. If he has a cape, it'll also add the effects of the spinning cape as well.
You can grab items on Yoshi by landing on Yoshi and grabbing the item on the same frame. If the item is not a springboard, however, it must be in a lower sprite slot than Yoshi.
If Mario grabs a shell, throwblock, or goomba on Yoshi, he'll be knocked off almost immediately as if Yoshi took damage. Note that this will not occur if the sprite is eat-canceled.
If Mario is running in the same direction as a shell while riding Yoshi, he can pass slightly inside the shell from behind without taking damage from it, until either the shell turns around or he passes far enough inside that he's considered to be in front of the shell.
Yoshi's fireballs can be destroyed by a capespin mostly regardless of the vertical between them and Mario; the only thing that generally matters is his horizontal distance from them.
Yoshi has an unusual hitbox that makes all standard clipping glitches have a significantly lower speed requirement. More info
If Mario is riding Yoshi in water while big, you can clip into the right side of blocks occasionally by just swimming into them.
While riding Yoshi, Mario can clip upwards through solid blocks by landing on an item near it.
If a Yoshi is one tile below the top of a ledge, Mario can land on him if he clips far enough into the top of the block while Yoshi is bouncing upward.
Landing on Yoshi at the right angle next to a solid block may clip Mario inside the block.
Landing on Yoshi while he's inside a springboard and immediately dismounting him will allow Mario to pick up the springboard.
Jumping at the right angle onto a message box or light switch while riding Yoshi will "suck" Mario on top of the box, even if there is a solid block on top of it. He also won't be able to be crushed while on top of it, though you won't be able to get out otherwise.
If Yoshi ends up inside a block, you will be unable to move out of the block without jumping.
Yoshi's swallow timer while he has a sprite in his mouth normally decreases once every frame. Freezing the game (via $9D) on one of the decrementing frames, however, will cause the timer to decrease every frame while the game is frozen.
After eating enough berries, you can delay Yoshi's "laying" animation by not touching the ground for more than a frame. If you throw Yoshi in a hole before he lays it, the next-spawned Yoshi will lay it instead.
The egg Yoshi lays can be used to hit blocks.
If Yoshi eats a powerup as it's rising from a block, Mario will not actually be given any powerups.
Spinjumping onto Yoshi and then dismounting him the frame Mario lands will cause Mario to spinjump off of Yoshi, yet have the height of a regular jump off of him.
Dismounting Yoshi on the frame he gets damaged will cause Mario to gain invincibility frames as normal without Yoshi running away.
If you land onto Yoshi after gaining flight without touching the ground, you can continue to fly while riding him, though the controls will be a bit strange.
Yoshi can make a powerup count as two powerups if Mario grabs the powerup while it is stuck to Yoshi's tongue.
Non-carryable sprites that get eaten by Yoshi are actually erased one frame prior to his tongue fully retracting, allowing you to pick up a second sprite if Yoshi's head passes by it. One well-known use of this is for quickly eating Pokey segments.
If Yoshi is despawned with a sprite in his mouth, that sprite will persist despite no longer "existing". It's impossible to despawn the sprite in this state, so the slot essentially becomes useless.
If a sprite on Yoshi's tongue despawns before it is pulled into his mouth, the game will register that sprite as having been eaten, but will still respawn the original sprite. This can also be abused with shells to turn a single shell into many, or in a similar manner with powerups.
Yoshi's tongue will have unusual interacting when crossing screen borders. When crossing offscreen, it will loop to the opposite side of the screen, allowing you to pick up items on the other side. When crossing onscreen, it will "compress" toward Yoshi. An interesting advantage of this is that jumping off Yoshi when it's compressed will let Mario grab the sprite as he's jumping off. Doing this at the bottom of the screen can potentially cause the sprite to register as having despawned before Mario grabs it, allowing you to duplicate the sprite.
Invisi-Yoshi: Spawning more than one Yoshi onscreen will cause all Yoshis other than the one in the lowest sprite slot to turn invisible and have unusual interaction. Video
Dismounting an invisi-Yoshi will cause Mario to warp to whatever its Y-position was when he mounted it. It should be noted that Invisi-Yoshi can still move for a few frames after jumping on him, and can also be sent running if touched with a thrown shell, meaning its Y-position (and where Mario warps) can be changed. Should also be noted that invisi-Yoshi can be landed on mid-fall.
If Mario is riding a visible Yoshi when a second Yoshi hatches, Mario will be riding an Invisi-Yoshi but will retain his riding animation and will keep Yoshi's hitbox. He also won't be able to take damage from most enemies.
Dismounting a visible Yoshi in a level with more than one Yoshi spawned when entering the death zone underneath the level will cause Mario to warp to the next visible Yoshi's Y-position, and will receive the same effects described in the previous glitch. However, unlike the previous glitch, Mario will be unable to jump off this Yoshi.
While Mario is in the state described by the previous two glitches, Yoshi's will be unable to despawn from the level. This mean, if a Yoshi falls off the bottom of the level, it will not be despawned by the death zone, and will instead loop vertically all the way around the level. It should be noted, though, that it takes about 18 minutes for Yoshi to complete this loop.
When Mario is in the aforementioned "riding Yoshi" state, getting hit by a cluster or extended sprite will release Mario from the state, and will cause the visible Yoshi to start running. If he was riding an invisi-Yoshi at the time, he will still be riding that Yoshi. It's also worth noting that the visible will always start running at a slower speed than normal when hit by those sprite types.
When there's more than one Yoshi spawned in a level, the eggs laid after eating enough berries will spawn at the Yoshi in the highest sprite slot. Because the visible Yoshi is always the lowest slot, this means it will end up laid by an invisi-Yoshi.
Killing the visible Yoshi will cause the next invisi-Yoshi to become visable; if Mario is riding this Yoshi, it will appear one tile below him, allowing him to fall through the ground. Also, if Mario is climbing when the Invisi-Yoshi becomes visible, he'll continue to climb despite riding Yoshi at the same time.
If the visible Yoshi is killed while it has an item in its mouth, the next visible Yoshi will spawn with a nonexistant null sprite in its mouth. When spat out, "nothing" will come out of Yoshi's mouth. More info
Double-Tongue Glitch: If Yoshi spits out his tongue on the frame Mario transforms, Yoshi will stick out his tongue twice, regardless of if he swallows anything. This can also be done remotely to an Invisi-Yoshi (x), which can be carried over through pipes as well (x). As an alternative, this glitch can also occur when taking damage while riding Yoshi without getting knocked off (by munchers/spikes, Wigglers, Dino Rhinos, etc.). More info
If Yoshi swallows a sprite on the first tongue of the above glitch and nothing on the second, he will have a nonexistant null sprite in his mouth.
When doing the double tongue method of creating a null sprite, any sprite grabbed by the first tongue will no longer respawn, as if it was destroyed.
If $019D (part of the stack) is a value from 00 to 0C and Yoshi has a null sprite in his mouth, then Yoshi will get wings or be able to stomp the ground based on $16F5 (score sprite high X position). You can manipulate this value at any time, allowing Yoshi to freely swap out powers.
Powerup incrementation: Spitting out a null sprite while on a brown revolving platform will cause unintended effects; one common effect is increasing Mario's powerup status, even past the standard values. Collecting powerups in these additional sprites can have a number of differing effects, from crashing the game to giving you a goal sprite. More info - Effects - Goal item data - Video
Null sprite overload: Spitting out a null sprite will glitch certain sprites' properties. Slot #3 will usually lose ground interaction, and slot #1 will usually either become burnable or change its interaction completely. More info
Burning a Yoshi (via overload) on the frame Yoshi's tongue timer ($14A3) is equal to #$0C will cause the coin spawned by burning him to turn into a sprite berry.
Unstepping a sprite: Hitting a sprite and swallowing it before it fully disappears will reset it to its initial state.
Swallowing a springboard at the same time Yoshi is bouncing off it will give him a large boost while bringing the spring with him. This boost can be extended by holding up and/or B, and can even go through solid blocks. It will also give the springboard a slightly glitched graphic when spat back out. Video - Fix
Eat-canceling an item: If Mario is hit off of Yoshi while an item is stuck to Yoshi's tongue, that item will be dropped off of it while retaining any properties it had while stuck to the tongue. This can allow for a variety of effects, including causing sprites to lose (some) vertical object interaction, moving normally immovable sprites, and more.
If Yoshi has an item on his tongue and you jump off of him as he is about to despawn, the item on Yoshi's tongue will be eat-canceled and warp to Mario's position as he jumps, allowing him to pick up carriable items or doublegrab powerups (shells are an exception; Yoshi will instead bounce off of it). It will also be counted as a new sprite, meaning the original one will respawn as well. Note that Yoshi has to despawn before the sprite for this to work, as it's still stuck to his tongue until then.
Not only does an eat-canceled sprite lose damage interaction with Yoshi, its entire slot does as well, until the next time Yoshi sticks out his tongue.
Eat-canceled sprites won't interact with sprites in a higher slot than them.
If a shell is eat-canceled, the shell will fall through the ground when kicked. Additionally, eat-canceled shells won't knock Mario off of Yoshi, and can also be doublegrabbed without destroying each other.
If a key is eat-canceled, sticking it in just below an inner corner will allow Mario to walk on the key through solid blocks, regardless of his powerup status. This can also be done with springboards, though Mario will be unable to pass all of the way through before being crushed.
If any carriable sprite is eat-canceled, throwing it upward while it's in a wall will cause it to slowly sink downward. It can still hit blocks as it's sinking.
Item swap: Mario can briefly create a null sprite on Yoshi's tongue by destroying or despawning a sprite while it is stuck to it (it should be noted that burning a sprite and collecting its coin, as well as grabbing a Koopa on Yoshi's tongue as it jumps into a shell, are both valid methods). Doing so will cause the next sprite to spawn in the null sprite's slot to warp to Yoshi's tongue. This can be used for a variety of effects, such as messing with sprites that change properties based on position, since this glitch essentially changes a sprite's spawn position. More info
Certain sprites have the "give powerup when eaten" flag set despite not being powerups, most notable of which being the Chucks. Depending on Mario's powerup status, using item swap to eat these sprites will give Mario odd sprites in the item box. Two particularly well-known uses are getting a goal sphere from a Clappin' Chuck when Mario has a fireflower, and getting a Lakitu cloud from Chargin' Chucks when small. More info - Data Table
You can "store" an item swap on an Invisi-Yoshi's tongue by sticking a sprite onto a visible Yoshi's tongue before it's replaced by another Yoshi. When the invisible Yoshi becomes visible again, Yoshi's tongue will spawn with it and grab whatever sprite happens to be in the same slot as the one that you stuck to it before.
If there is no sprite currently in the slot stored to the Invisi-Yoshi's tongue, then it will instead spawn a copy of the last sprite in the slot. Since this counts as a new sprite, it can be used to duplicate any sprite.
If a sprite is stored to invisi-Yoshi's tongue, spitting out the visible Yoshi's tongue a few frames before it despawns will cause a second tongue to spawn on Invisi-Yoshi, resulting in a null sprite.
After item swapping, sprites can then be eat-canceled off of Yoshi's tongue. Certain sprites that are never meant to be edible by Yoshi can create some unusual glitches as a result.
If Yoshi starts to sink in lava while a sprite is stuck to his tongue, and that sprite is then destroyed, Yoshi will have a null sprite on his tongue and be able to perform an item swap. A difference between this and the normal item swap, however, is that the sprite will remain stuck to Yoshi's tongue while he's sinking, which can be combined with Yoshi's tongue interaction on screen borders to create a few interesting effects. The sprite will also be automatically eat-canceled when Yoshi disappears.
Priority swap: If all sprite slots in division 1 are filled, then prioritized sprites such as the goal sprite will have to replace another sprite in order to spawn, and the sprite it replaces can manipulated by abusing priority through sprite permanence. In simple terms, priority sprites will replace the highest non-permanent sprite slot if all of them are filled. If that sprite happens to be stuck to Yoshi's tongue when the priority sprite spawns, the priority sprite will actually warp to Yoshi's tongue, even if it's a stationary sprite like a goal tape. More info
Eat-canceling a goal tape will set its max height to wherever it was dropped, which can lead to some strange side effects. That game still registers its original position as the actual sprite, so touching the goal tape below what would normally be the 1 star mark will actually give a glitched number of bonus stars, even greater than 50.
If you item swap a sprite that uses extra bits (e.g. the goal tape) when Yoshi is in a higher slot than it, the sprite's extra bits will be modified. The game normally stores the extra bits with the sprite's high Y spawn position (in the format %----EE-Y) before correcting it in the sprite's initilization code; if Yoshi's tongue's code runs before the sprite's does, it will instead use the high Y position from the tongue, affecting the extra bits in the process. NOTE: this glitch will NOT work in hacks that use custom sprites, due to using a specialized table for extra bits. More Info
Suicide swap: Yoshi uses $C2 as a flag to decide whether Mario is riding him or not. If Yoshi despawns on the same frame another sprite spawns, and that sprite sets $C2 to 01 on spawn, then the game will think Mario is riding the sprite like a Yoshi and warp it to his position. In addition, when Mario goes to another room or level, the game will spawn him on a Yoshi which will have a different palette or graphic depending on the sprite that was swapped. More info - Video
Suicide swapping a mushroom on the same frame Yoshi swallows a sprite will cause the mushroom to turn into a sprite berry. Video
Stunning a sprite: If Mario spits out a sprite while its stun timer is set, it will spawn an extra sprite once its stun timer hits zero. While this is intended for sprites like the Koopa shell, it works for other sprites, as well. For example, P-switches can spawn a fish if Yoshi spits it out when it turns into a smoke cloud. More info
Spitting out a stunned Koopa shell on the frame its stun timer is about to run out will cause the Koopa spawned by it to be sent flying as if it were knocked out of the shell.
Yoshi can "store" a sprite slot in his mouth, but it gets a bit complicated. First, do the double tongue glitch and pick up a carriable sprite with the first tongue. Then, with the second tongue, pick up the sprite you want to stun, but eat-cancel it before Yoshi swallows it. As a result, Yoshi will have the second sprite slot "in" his mouth, but other sprites can still spawn in that slot and will function as normal. Yoshi can then spit out that sprite (resulting in a glitched version of it), or swallow it (resulting in the sprite vanishing).
With the above glitch, you can also stun sprites that are normally unstunnable. You just have activate the sprite slot's stun timer and then spit it out of Yoshi's mouth while the timer is active. This can create a variety of effects, most notably a Koopa Kid from a sliding blue Koopa, a goal tape (at x=0,y=0) from a Pokey, a keyhole from a Dino Rhino, and a Reznor from horizontally-swimming fishes. Video - More Info - Data Table
When spit out of Yoshi's mouth, stored sprites begin acting like a shell, yet still retain the object interaction of the original sprite. This leads to some odd block interactions for certain sprites, such as Pokeys (five tiles higher) or Piranha Plants (one tile lower), and even affects block duplication for these sprites.
Spitting out a stored sprite when its stun timer is nearly 0 will cause the sprite spawned from it to act as if it was spat out of Yoshi's mouth. For most sprites, this will make the sprite kickable as if it were a flopping fish, but it can have some odd additional effects on certain sprites.
If a sprite gives special properties to Yoshi when in his mouth (e.g. blue or yellow shells/Koopas), then storing that sprite in Yoshi's mouth via the stun glitch will also inherit those properties to Yoshi until either the sprite gets overwritten or Yoshi swallows the storage. In the case of wings, the wing graphic will also not show up, nor will the flight sounds play.
If you kill a Yoshi and then spawn a second one, the new one will inherit the first one's "state" (sticking tongue out, laying an egg, etc.) that it had when it died.
If Yoshi has a key in its mouth, dying while riding will still let Mario enter any keyholes he passes on his way down.
If a keyhole is in a higher slot than a key, grabbing the key while it's stuck to Yoshi's tongue will allow the tongue to activate keyholes (even through walls). An easy method of doing this is by storing the key's slot to an invisi-Yoshi's tongue.
Hitting a goal tape while a shell is stuck to Yoshi's tongue will make Yoshi act like he has a yellow shell in his mouth during the walk, regardless of what color the shell actually was.
If Yoshi has the stomp power from yellow shells and he lands on Layer 2, the smoke and quake sprites will not scroll with Layer 2 and will instead spawn at the position it would be at were Layer 2 not scrolling. This occurs both horizontally and vertically.
If Yoshi eats a powerup as Mario dies, Mario will "revive" and bounce upward. The speed given varies depending on how far Mario is into the death animation when Yoshi swallows it.
If the above is done when the time limit for the level reaches 0, the timer will also stay at 0 as if it was set to such when Mario entered the level.
If Yoshi swallows a hundreth coin as Mario is dying, the game will register Mario as dying but will not decrease the life counter. This can be used to "survive" a game over; the game will still show the game over screen, but Mario will reappear on the overworld as normal.
Layer Switch Glitch: If Yoshi eats a powerup and transforms Mario as he is entering a pipe, Mario will stop entering the pipe and several different effects will occur. Mario will go behind Layer 1 and no longer interact with any sprites except Yoshi and platforms, and his climbing graphic will be glitched. Yoshi will be stuck in his "turning" frame, and while his tongue will still be able to interact with things, it will be invisible and he will be unable to duck. Thirdly, certain sprites which were not burnable before will become burnable, such as Yoshi, sprite coins, powerups, and the goal tape. The opposite is also true, with enemies such as Koopas and shells becoming unburnable. It should be noted that Mario can end up on an invincible Yoshi if he burns Yoshi while he's riding it.
If Mario is holding an item when he switches layers, the item will become stuck to Mario and he will be unable to let go of it, even if Y and X are released (this also means Yoshi can not be ridden). In addition, if Mario goes to another room, this item will be taken to that room as well, even if he doesn't enter through a door; it will appear at whatever position it was at when Mario exited the previous room.
If the layer switch glitch is done frame-perfect, Mario will retain sprite interaction and sprites will retain their correct properties, but Yoshi will still glitch and still go behind layers and have glitchy interaction while being ridden. In addition, in this state, if Mario picks up an item, it will be stuck to him as described above.
If Mario is riding Yoshi as he comes out of a pipe downward, holding up will allow Mario to re-enter the pipe immediately.
If Mario is riding Yoshi while big as he comes out of a pipe downward, and there is ground two tiles below the pipe, dismounting Yoshi on the first frame the player gains control will drop Yoshi into the ground.
Dismounting Yoshi repeatedly against a ceiling will let Mario move horizontally (albeit slowly) without moving vertically. This can be used to clip into upside-down slopes.
Riding a Yoshi into a Mode 7 battle will cause Mario's ground interaction to be one tile higher than it should be. In the Iggy and Larry battles, this doesn't cause any major problems, but in Roy's, Luwig's, Morton's, and Bowser's rooms, Mario will fall through the ground and die if he doesn't jump off.
When Yoshi eat-cancels a Pokey segment, its Y speed constantly increases, causing it to "bounce" if its dropped from a height of y=11 or higher. Yoshi can then eat this bouncing segment infinitely without it actually disappearing, and because it counts as a separate sprite, Mario can turn one Pokey into five individual sprites. Additionally, the segment slowly rises upward at a rate of 8 pixels per bounce, and after about two hours, it'll disappear from looping around the screen.
If Yoshi's tongue comes into contact with part of a pokey while sprite slots are filled, then that part of the Pokey will just completely vanish without being counted as stuck to Yoshi's tongue. This allows Yoshi to very quickly erase the Pokey, as every frame his tongue is in contact with it will cause another segment to disappear.
Holding both left and right at the same time while riding Yoshi will cause him to continously turn back and forth while moving rightward.
While riding Yoshi, Mario can slide up slopes by holding down and pressing left/right. This will also allow Yoshi to travel across purple triangles without bouncing upward.
If Mario jumps off of Yoshi while he is eating Yoshi wings, Mario will still fly up to the Yoshi wings room without a Yoshi.
While in the Yoshi wings room, opening Yoshi's mouth (to stick his tongue out, spit out an item, etc.) will cause his wings to temporarily disappear; you can't fly during that period, but you'll fall faster.
Taking Yoshi wings or obtaining a bonus game in a room that only uses secondary exits will take Mario to a glitched exit in the bonus game room rather than the room it's supposed to go to. Lunar Magic fixes this by default.
If Mario is riding on a Yoshi that has a blue shell in its mouth and he slides off of a sprite platform, you'll be unable to control Mario's horizontal movement until he hits something and stops. Video
When Yoshi has wings from a blue shell and the current level has some form of vertical scrolling enabled, the screen will always scroll upwards to Mario, even if he's not actually riding the Yoshi. This means it'll even scroll up to Mario if he only lands on the ground for a frame, which it normally doesn't do. This effect also persists if Yoshi despawns with the blue shell in his mouth, and will continue until a new Yoshi spawns or a new level is loaded.
If Invisi-Yoshi exists in a level, swallowing a blue shell with the visible Yoshi will allow flight but will not display wings or play the flight sound effect, nor will the screen automatically follow him vertically.
If Mario is the "riding Yoshi" state on an Invisi-Yoshi and the visible Yoshi has a shell in its mouth, then the Invisi-Yoshi will receive the effects of that shell as well.
Landing on Yoshi counts as bouncing on a sprite. Jump off Yoshi enough without touching the ground and the next enemy you hit can give you a 1-up. Fix
If Yoshi's tongue stops touching a berry after it gets stuck to his tongue/mouth (either by turning or ducking), the berry will be eat-canceled as a permanent sprite. This can also be done by baby Yoshi by turning on the frame he comes in contact with the berry, or by passing the berry while he's in the process of eating another sprite.
If Yoshi runs into a berry on the same frame his tongue picks it up, the game will give two coins.
You can "store" a berry to Yoshi's tongue by picking up a berry with Yoshi's mouth, but canceling it by sticking out Yoshi's tongue and turning away. You can tell if it was done correctly if the berry doesn't turn into a sprite, but the game still freezes for a frame as if Yoshi ate it. As a result, the next sprite Yoshi swallows will add to his berry count, and can be repeated on a single berry indefinitely. A small additional side effect is that any sprite berries will inherit the palette of the stored berry until it is used. Video
If Yoshi has a null sprite in his mouth, passing his mouth by a berry will cause him to store the berry to the null sprite (giving him a berry when he swallows). During certain frames of the swallowing animation, you can also actually eat the berry instantaneously as opposed to storing it.
If a berry is located at the very bottom of a subscreen, then picking up the berry with Yoshi's mouth while he's ducking with his tongue out will cause the berry to register as eaten without actually clearing the tile. This can then be repeated infinitely.
Berries don't work correctly in vertical levels. Yoshi will be unable to eat them most of the time, and when he can, they won't disappear; instead, an empty green bush tile will appear a screen below the berry's actual position, and the berry itself can be eaten an unlimited number of times.
When Yoshi eats a berry by running into it, the game will adjust Mario and Yoshi's position slightly during the freeeze to center him on the block. If the berry is placed close enough to a slope, this can be used to clip them into the slope.
If Yoshi ends inside a block without Mario riding him, he will "climb" the blocks upward until he reaches an empty block. This can occur as a result of growing Baby Yoshi inside the block, spawning a block on top of Yoshi, or clipping four pixels into the block and dismounting. Video
In the Japanese version of SMW, Yoshi is able to eat the jumping dolphins. This is not possible in any other release.
If a Baby Yoshi and adult Yoshi are spawned in the same level, Yoshi's head graphics will glitch and the game will have some strange effects. One effect in particular is that berries will not actually be eaten when Yoshi's head touches them; the game will keep registering him as eating it, but it will never disappear, letting you get an infinite number of berries.
If both Baby Yoshi and Yoshi eat the same item, Yoshi can still spit out the item, but it will have glitched properties. Strange effects can also occur from two Baby Yoshis eating the same items. This can additionally be used to create a null sprite.
If Baby Yoshi swallows multiple enemies consecutively, the game may register him swallowing an extra non-existant sprite; this can be used to grow a Baby Yoshi with only three sprites.
While Baby Yoshi is swallowing a shell, it's actually just temporarily moved to the background rather than having sprite interaction disabled. This means you can use it to kill climbing Net Koopas behind a net from the in front of it.
If Baby Yoshi grows as he is eating a sprite, that sprite will be eat-canceled. This can also result as a side effect of eating multiple sprites consecutively, meaning, although you need at least three sprites for it, the last sprite may not actually be eaten.
If Baby Yoshi swallows a non-permanent sprite while far enough offscreen, the sprite will despawn as he is eating it. This will allow said sprite to be allowed to respawn even though it was used to feed Yoshi, making it possible to grow him with just a single enemy. Additionally, this effect can be used to item swap.
If Baby Yoshi grows close enough to a ceiling and Mario lands on the Yoshi while it's still next to it, Mario can jump straight off of Yoshi and through the ceiling (regardless of his size). Alternatively, you can be forced far enough into the ceiling such that Mario can clip through corners where the ceiling and left wall meet, retaining Yoshi in the process.
If a Baby Yoshi is on screen 01 of a level, spawning a throwblock in slot #2 on screen 00 at the same screen position as the Baby Yoshi will cause the Yoshi to register and eat the throwblock.
Baby Yoshi can swallow sprites as they're rising out of a block. If thrown at the right angle, Baby Yoshi can even hit a block and eat the sprite that comes out of it in a single throw.
Useless
Having a Yoshi on the same screen as a Podoboo will glitch Yoshi's head graphics. His body can also be glitched by the splash created by lava.
When riding Yoshi, Mario will not interact with the bottom tile of a Banzai Bill.
While turning on Yoshi, one of Mario's feet is non-existant and can be seen through.
Mario can still be knocked off of Yoshi by a Boo ceiling even when he has a star.
While Yoshi is laying an egg, you can press X or Y repeatedly while riding him to play his tongue sound.
If you stick out Yoshi's tongue before Mario hits a goal tape, you can duck or stand up during the walk animation as long as it's out.
Yoshi can still duck or even spit out sprites during any period where the game is temporarily frozen from $9D (including keyholes).
When spawning multiple Yoshis, the newest Yoshi will hatch twice as fast as the last-hatched Yoshi.
Taking damage on the same frame Yoshi hatches will cause Mario's shrinking animation to speed up.
If Mario dies on the same frame Yoshi hatches, the game will continue to function as Mario is dying, rather than freezing as normal. This can lead to some strange effects such as Mario freezing mid-fall, remounting Yoshi even as he dies, or dying a second time due to an enemy or time up.
Yoshi's tongue turns invisible while entering a pipe, but will still pull sprites around. However, it will behave strangely as a result of the tongue not actually being drawn.
If Mario dies on Yoshi while Yoshi has his tongue out, Yoshi's head may briefly loop to the top of the screen when they fall off the bottom of the level.
Yoshi can lick the brown revolving platform by sticking his tongue out to the right side of its base. It won't actually do anything besides make a noise, though.
Yoshi can lick the side-exit-enabled sprite by licking the center of the screen, three tiles from the bottom. It won't actually do anything besides make a noise, though.
If Yoshi eats the directional coin sprite, the music will never change back.
Occasionally, eat-canceled berries may take the place of powerup graphics.
Collecting a green berry after the music speeds up from time running out will increase the timer while keeping the music at its speed; the effect can then be repeated indefinitely. Fix
If Yoshi's head eats a green berry while Yoshi is ducking and sticking out his tongue, his head's graphic will glitch slightly.

Item and Object Glitches
Items can get stuck in walls, and will spasm while inside.
Items stuck in walls can be moved around by scrolling the screen on the right frames.
Items can be forced through solid blocks by entering it far enough before releasing. Video
If an object is tossed high enough off the top of the screen, it will despawn.
Items will not interact with blocks if they are 8 or more pixels offscreen on the left side or 12 or more pixels offscreen on the right. When even a pixel offscreen on the left, the hit animation will also not appear.
Items can fall through slope corners if they're moving fast enough at the right angle. Shells can also do this occasionally just by riding up the slope.
Taking a pipe exit to a normal entrance while holding onto an item will cause Mario to release the item upon entering the level, spawning it at whatever position the pipe exit was in the previous one.
Double-grabbing: Mario can pick up two items at once if they're the right distance apart. Due to oddities in the way springboards are handled, you can grab more sprites at the same time if at least one of them is a springboard. Fix
Although shells usually kill each other when doublegrabbed unless they're eat-canceled, they can safely be held together if Mario enters a pipe at the same time. They will kill each other on exit, however.
Items can also be carried while Mario has a P-balloon by grabbing both on the same frame.
Items can be carried while climbing, sliding, or flying by simply grabbing the item without getting off, jumping, or stopping flight. Note that the one exception to this rule is the moving rope mechanism, which Mario will fall off of when grabbing an item. Fix
Carried sprites won't actually flip to the other sides of nets with Mario, but the game will still let him hold it through the fence.
Items can be released while flying without stopping flight by letting go of Y for a single frame some time after catching air.
If Mario gets between two solid carryable sprites and a wall, he will be pushed into the wall and be crushed. If you're big, it's also possible to spinjump through the floor before he dies.
Mario can jump through ceilings while big if he stands on two solid carryable sprites while they are close enough to said ceiling. Alternatively, you can use Yoshi and a single solid sprite for the same effect. This can also be done while small and with just a single key or springboard if they are moving upward toward the ceiling as Mario lands on it.
If Mario is big, landing on a key close to the ceiling will cause his head to enter the ceiling enough to push Mario leftward, even through solid walls.
Mario can enter through doors and pipes while he is standing on any solid sprite.
Any of the solid carryable sprites are able to damage a Pokey on the frame they are thrown.
Keyjump: Mario can land on and jump off of a key while it is in midair. Note that if the key is falling too fast, this glitch may not be possible. Video
If two keys are spawned at the same time, only the key in the lowest sprite slot will be able to interact with keyholes.
If Mario is standing on two keys at the same time, he will be unable to jump until he gets off of one.
Mario is unable to walk in a one-tile space below keys, even if he's small or ducking.
P-switch jump: Mario can land on and jump off of a P-switch on the first frame he hits the top of it. Video - Fix
Carrying a silver P-switch through a pipe will make it act like a blue P-switch in the next room. Note that if another sprite in a lower slot is doublegrabbed on top of the silver P-switch, this glitch will not take effect. Fix
If a pressed P-switch despawns before it disappears in a cloud of smoke, then the switch will respawn as if it was not pressed.
Mario will still bounce off of a springboard even if it moves out from beneath him.
Springboards will disable Mario's interaction with both blocks and sprites while he is stuck on it, allowing him to fall through corners or platform sprites. You can also be pushed through ceilings due to this, if Mario throws up a springboard and is able to land on it as it is rising. This can most easily be done in any 2-3 tile high space. Video
If Mario is big and standing up, he'll be unable to jump through the bottoms of springboards. If he's small, ducking, or riding Yoshi, however, this won't happen.
If a shell is spinning in a one-tile space, it will become invincible to all quake sprites (including capespins, Yoshi stomps, and hit blocks) until it exits the space.
Throwing a shell upwards on the frame it is about to sink in lava will cause it to reset to it is initial state. In other words, it'll suddenly have a Koopa inside it. On the frame the shell touches the lava, Mario can also bounce off of or be damaged by it, as well.
You can perform the above glitch with other carryable sprites by getting said sprite in slot #1 and overloading it. This will have some odd effects on the sprites when they're reset, such giving a key wings or changing a P-switch into a gold switch (acts like a blue switch, though).
Mario can throw a shell up even as a Koopa is entering it, allowing him to effectively move Koopas throughout the level. Note that red and blue shells will invert their speed when the Koopa actually spawns. Similarly, if Yoshi eats a shell as a Koopa is entering it, spitting it out before its stun timer hits zero will still have the Koopa jump out of it.
If you restun a shell with a Koopa inside (by way of capespin/block hit/etc) just as the Koopa jumps out, the shell will end up restunning with another Koopa still inside, resulting in two Koopas overall.
Portable disco shell: If a Koopa enters a shell, releasing or throwing the shell upward on the frame the Koopa would normally appear will cause the Koopa to disappear and retain its shell form. If the Koopa that entered it was yellow, though, then throwing this shell will turn it into a disco shell.
Repeating the portable disco shell glitch with the same shell 255 times will cause the next yellow Koopa to enter the shell to get rejected immediately from it as if it were knocked out of the shell.
If another Koopa (other than a yellow one) enters the portable disco shell, the Koopa that is created will basically act like a normal yellow Koopa, but will act like a disco shell when bounced on. This Koopa can also be turned back into a portable disco shell by capespinning it. This new disco shell is unique in that it can be stopped at any time with a capespin, rather than being destroyed like a normal disco shell would. Video
Capespinning the special disco shell described above can also give a few unused colors of shells, such as gold, grey, brown, sky blue, teal, or pink. These colors will either act like a blue or yellow shell when eaten by Yoshi or when a Koopa enters them.
If a blue Koopa kicks a portable disco shell (thereby activating it), the speed of the shell will be much greater than it normally moves at.
If a Koopa tries to flip over a shell in a higher slot than it, it will usually be killed by the shell in the process.
Blue Koopas can catch Bob-Ombs, but on when they're either in a lower slot or on the ground on the frame they register interaction. However, the Koopa won't slide or stop the Bob-Omb's movement, causing it to be kicked from inside or behind the Koopa. It can even fly straight through him or make him turn around to face it.
When catching a throwblock, blue Koopas will sometimes end up killing themselves with it. Oddly, this also causes the throwblock's stun timer to reset, making it disappear as well.
If a shell bounces far enough into a blue Koopa, the Koopa will be killed by the shell as soon as it kicks it. This can also be forced by screenscrolling as the Koopa is catching the shell.
If a shell is registered by a blue Koopa but does not actually stop (due to bouncing off of a wall or otherwise), then the Koopa will be "dragged" along with the shell until the shell is either stopped or despawns.
If Mario grabs a shell that a blue Koopa is about to kick, and then lets go or throws it upwards before the Koopa kicks, the shell will still be kicked by the Koopa even if it's not actually touching it.
Screen scrolling as a blue Koopa catches a shell that has a Koopa inside will cause the Koopa to be flung out of the shell.
While any Koopa is in their kicking animation (including to flip a shell over), they will not be affected by gravity and won't move with the layer they're standing on. When on a scrolling Layer 2, this can cause them to end up inside the layer, as well.
Yellow Koopas will jump as if a shell was thrown at them so long as a shell is thrown in close proximity to them, even if it's being thrown away from them or bouncing off of a wall.
Yellow Koopas will also jump if any other carriable sprite is thrown next to them, so long as they are in close enough proximity on the frame the sprite is thrown.
If you capespin or bounce a shell that a yellow Koopa enters before it turns into a disco shell, then the Koopa will instead change colors to whatever color the shell is.
Shells will ignore the bottoms of blocks while they are spinning.
Carrying a buzzy beetle shell or a shell that has a Koopa inside it through a pipe will cause the Koopa/Beetle to never emerge from the shell. Note that if a sprite in a higher slot is doublegrabbed on top of the shell, this glitch will not take effect.
Throwing a Goomba upwards as Mario is colliding with a wall may cause it to warp upwards several tiles.
Landing on a Goomba, Bomb-Omb, or Koopa while flying will squish it with a glitched graphic rather than the regular actions they take.
Shells, throwblocks, Goombas, and Bob-ombs can destroy sprites that would normally be undestroyable (e.g. Thwomps, Thwimps) so long as they are in a higher sprite slot than the sprite.
Dropping or kicking a shell or Goomba on the frame that an enemy is about to collide with it will destroy the other sprite without destroying the shell/goomba, and will give 1000 points as if they actually had collided.
Flying ? blocks will destroy shells, Bob-Ombs, Goombas, and throwblocks if Mario runs into the block while holding them.
Throwing a carryable sprite at a flying ? block will zero its Y speed upon hitting it. Alternatively, its X speed will be zeroed if it is thrown up at the block. And if it's dropped on top of the block, it will fall through while still hitting the block.
Flying ? blocks will invert the X speed of throwblocks when hit, essentially bouncing the block back in the previous direction, rather than making them break.
The bottom of flying ? blocks are also treated the same as the sides of it, meaning the X speed of sprites thrown upward at it will still invert.
If Mario collects a star while holding an item that would normally be destroyed by star power, that item will not be destroyed unless Mario lets go of it and touches it again.
Mario can pick up a throwblock on the same frame he jumps off of it.
Dropping a throwblock just as it's about to disappear will extend its timer a short time.
If sprite slots 0-9 are filled, Mario will be unable to pick up throwblocks.
Throwblocks will bounce backward when thrown at a very steep vertical slope. You can even make it bounce back and forth infinitely if you throw it between two of them.
Landing on the very top of a very steep slope for a frame will boost Mario's speed, allowing him to get up to 51 speed without a cape. Normally, the slope would slow Mario to 32 when going down it.
Mario can spinjump off of throwblocks after they're thrown.
Carrying a throwblock, Goomba, or Bob-omb through a pipe will make it never run out of time. However, if you double grab the sprite with another sprite in a higher slot, this glitch will not take effect.
Horizontally kicking a Goomba, Bob-omb, or Mechakoopa will reset their stun timer; this can also cause the Bob-omb to change palettes if you kick it while it's flashing.
It's possible to bounce off Bob-ombs, Goombs, and Mechakoopas a frame before their stun timers run out. This is most notable with Bob-ombs, since you can't normally bounce off them again after they're stunned for the first time.
When Mario grabs a sprite, its X and Y speed doesn't get reset; this instead happens when he throws or drops it. However, sprites that hop out of Mario's hands on their own, such as Goombas, Buzzy Beetles, or MechaKoopas, don't get their speeds reset. One use of this is allowing Mario to bounce off the sprite in mid-air without needing to let go of it.
For a few frames after being thrown, a Goomba will destroy other sprites without being destroyed as well.
Explosions from Bob-ombs can still be spinjumped on, as well as capespinned and killed. Fix
Mechakoopas will pass through the bottoms of solid blocks while active. In other words, you can just throw it up as it's about to reactivate to send it through the roof.
Hittable blocks will always bounce sprites away from Mario when hit, regardless of which side of the block Mario is actually on.
Hitting a block twice within its activation frames will cause it to dispense two items.
Capespinning a block at the same time that the game is frozen (via $9D) will cause the block to dispense multiple items, usually filling up every sprite slot available.
Block duplication: Throwing an item into a hittable block in the right spot will cause it to "duplicate" the tile to an adjacent block, either horizontally, upward, or diagonally upward. Fix - More info
In levels with a scrolling Layer 2, it's also possible to duplicate downward or even two blocks downward.
Duplicating a block into a Yoshi coin and then grabbing the Yoshi coin will turn the block into tile 125; this tile has the potential of spawning a key, Yoshi wings, P-balloon, or shell. Note that if the block you duplicated was a turnblock, you'll have to wait for it to stop turning before collecting the coin.
Block factory: Items can be forced into corners or walls and get stuck inside. If one of the blocks it's stuck between happens to be a hittable block, it's possible that it will create a situation in which the block is rapidly duplicated until the sprite despawns or is removed.
The above can have a few strange effects on other hittable blocks; bounce sprites may get overwritten so that the blocks turn into an invisible solid block, or they won't spawn for a frame and will dispense two items at once, or won't spawn at all and can dispense an item without being registered as hit. If a noteblock's bounce sprite gets overwritten while you're bouncing on it, Mario will also fall through it. These effects can also be created without block factory by spawning more than four bounce sprites before any of their animations finish.
Mario can fall through the top of block factories regardless of the block being duplicated, and can pass through it in either direction.
Tile 125's shell will only actually come out if an adjacent block knocks it upward.
Mario can still hit blocks while moving downward, so long as he enters the lower corner of the block enough.
If a block overwrites a rotating turnblock (e.g. by vine, duplication, etc.), then the turnblock will reappear once it stops rotating.
Turnblocks can be copied from Layer 1 to Layer 2 or vice-versa by interupting their bounce sprite (even during the rotating animation) with one from a block on the destination layer.
If there is a coin on top of a block when Mario hits it, the coin will become a solid, invisible block. Fix
If a coin is placed 16 screens away from a block and one tile higher than it, then bouncing off the top or side of this block (e.g. with noteblocks or the side-bounce turnblock) will give Mario a coin and create an invisible solid block on top. This occurs regardless of which side of the blocks the coins are actually on. However, the exact position of the coin needed for the glitch may vary depending on what screen it is on.
Hitting a block that uses bounce sprites in multiple directions (such as the all-way noteblock) on two sides at once will generate multiple bounce sprites even though there should only be one.
If the sprite in the lowest filled sprite slot with object interaction is inside one of tiles 021-024 or 121-124, then all tiles outside of the level will register as the corresponding tile on Map16 page 0. They won't actually become solid when hit, but they will block Mario from below and spawn any related sprites. Notably, capespinning will briefly interrupt this effect.
Mario can pass through invisible coinblocks or noteblocks without hitting them as long as he is being pushed upward by anything other than a jump, including keys, platform sprites, ropes, or another layer.
Bonus game coinblocks will always register a correct hit if a shell, Goomba, or Bob-omb is knocked into it by a capespin or bounced by another block.
In a bonus game room, hitting a coinblock that isn't in one of the positions used by the original bonus game may cause additional brown blocks to spawn.
If a coinblock is placed too high in a bonus room, it will cause Mario to immitate a P-balloon when hit, except the P-balloon neither wears off nor can be controlled; Mario will only move with whatever inertia he had when the block was hit.
All multiple coinblocks function using the same timer to determine whether they continue giving coins or turn into a used block. This means hitting one, waiting a bit, and then hitting another will immediately turn it into a used block; the original one, meanwhile, will restart the timer when hit again rather than doing the same.
Releasing an item from the item box will cause it to continue cycling vertically throughout the level until Mario collects it. Its interaction will even loop every two horizontal screens as well, so you can grab even if you can't see it.
In vertical levels, permanent sprites will loop around vertically around the level. It takes about 400 in-game seconds for the sprite to make a complete loop, though. They can potentially also loop horizontally in horizontal levels, too, but only if they don't fall off the bottom of the screen.
In certain levels, objects will fall slower when off the top of the level, as if they are in water. The cause is unknown, but sprite buoyancy is likely related.
Useless
Finishing a boss battle while holding a carryable sprite will cause the sprite to disappear, but Mario will continue to act like he's holding it.
If you're standing on something after a boss battle ends, Mario will continue to stand there even if he shouldn't normally. For example, walljumping, P-switchjumping, keyjumping, or grabbing a throwblock all work, even though normally Mario would fall.
The game will register a bubble as being hit for every frame that a shell or throwblock touches it.
If a Koopa starts to jump into a shell while in the water and exits the water midway through the jump, the animation won't line up and it'll end up walking slightly further than it should.
If a shell, throwblock, Goomba or Bob-omb hit the very top of a Pokey's head, Pokey's head won't actually be hit, but a head graphics will still fall down.
If sprite buoyancy is enabled in a level, grabbing a throwblock will show the water splash graphic regardless of if it's actually in water.
When swimming with a carryable sprite in a level with sprite buoyancy, pressing against a wall will cause the game to think the sprite has exited the water and will display a splash graphic. Likewise, turning away from the wall will cause the game to treat it as entering the water again, also displaying one.
Grabbing an item on the frame Mario enters a pipe will cause him to enter the pipe without turning. You can also occasionally exit the pipe backward, as well.
Releasing of a pressed P-switch off the right side edge of a level will cause its graphics to briefly loop to the left side of the screen.
Turning while holding a Mechakoopa will cause Mario's head to disappear briefly.
Hitting a block above the screen will cause it to dispense whatever is inside and stop giving items like usual, but its graphics won't change.
Hitting a block off the sides of the screen will cause it to not register being hit.
Collecting a powerup on the frame a Yoshi egg lands on a block will cause its graphics to glitch briefly.
Bringing a carryable sprite into a Mode 7 boss room will cause the graphics to glitch.

Miscellaneous Glitches
Sprites will "slide" with inertia across tiles 1D8-1FF. It should be noted that this means if the sprite hits 0 speed while on one of the blocks, it will be unable to move at all unless Mario causes it to. Because the bottom tile of tileset-specific lava is also included in the range mentioned above, sprites can pass through it without being destroyed; only the top of the lava will actually kill it.
If enough sprites are close enough together, they can push each other off of or through blocks.
Screen scrolling on the frame that Mario touches a shell-less Koopa (other than blue) will cause him to kick and kill it.
Freezing the game (via $9D) on the frame that a shell-less red or blue Koopa touches the corner of a block will cause it to fall downward past that corner.
Koopas standing on a conveyor platform will continue to be moved while the game is frozen (via $9D).
If Mario knocks a Koopa out of its shell, lets it re-enter, and then knocks it out once more, the game will register that Koopa as a new sprite. This means, if the shell is then despawned, the Koopa will respawn, even if the shell-less Koopa you knocked out isn't. This means you can get an infinite number of shell-less Koopas from a single Koopa.
If a shell-less Koopa is jumping into a shell, and that shell despawns and is replaced by any other sprite overlapping with the Koopa, then the Koopa will enter the sprite and set two misc addresses for the sprite ($1558 to #$10, $160E to the ID of the Koopa). This can cause various effects depending on the sprite. More Info - Video
Sliding Koopas will stop sliding if Mario collects a powerup.
Sliding blue Koopas will only register the top of solid blocks; they'll pass right through the sides and bottom.
If a blue Koopa is prepared to kick a sprite, and that sprite despawns and is replaced by another carryable sprite within horizontal proximity of the blue Koopa, then the blue Koopa will kick that instead. If not a shell, this also sets that sprite's stun timer. Videos
Screen scrolling while a yellow Koopa is jumping will allow it to pass through solid blocks on the way up.
Yellow Koopas can still jump over shells while sliding. Combine this with the fact that sliding Koopas don't register the bottom of blocks, and you have a way to move a yellow Koopa upward through solid tiles.
The net-climbing Koopas will only actually hit Mario if his feet are touching them. This means Mario can just hang off the bottom of the net to avoid them.
Green net-climbing Koopas will not despawn off the top of the screen in vertical levels, essentially being treated as a permanent sprite. They'll still despawn below the screen, however.
It's possible to jump off the climbing net door during a few frames before it actually starts turning after being hit. Mario will still switch layers despite no longer being on the sprite, and grabbing onto something (even off the gate) will cause him to still be pulled around. Unfortunately, he still interacts with objects during it.
Getting pushed off the net sprite by a solid sprite (including two carriable sprites) right at the start of its rotation will cause Mario's X speed to rapidly start increasing in that direction. This will continue as long as he holds a net, eventually overflowing his speed and rebounding unless he lets go. Video
Feathers will not despawn offscreen unless they are falling. By way of an item swap, it is even possible to turn a falling feather into a permanent, still one.
Touching an invisible mushroom on the frame Mario's speed inverts will cause it to fly in the opposite directly than it normally would.
Stars push themselves far enough through blocks before bouncing off of them that Mario can collect a star through a corner between two blocks.
Spawning a Bullet Bill shooter on the far left edge of a level will not only cause it to not actually spawn, but also create a shell-less green Koopa at [0,0] in every available sprite slot.
Messages from a message box or display message sprite will erase whatever Layer 3 the level had; this includes water or smashers.
If Layer 3 water is replaced by a message box, the water will still have interaction at the bottom of the level.
Hitting a message box and then taking a screen exit will display that message in the next room instead.
Mario can land on the right corner of a message box or light switch for a frame in manner similar to walljumping, but without the speed requirement.
Being pushed inside a solid sprite (e.g. message box, turnblock bridge, Hammer Bro platform, Bowser statue...) will cause Mario to warp to the nearest side, even through solid blocks. If the camera moves sharply, this may also cause the newly loaded columns of Map16 to have glitched graphics until they're reloaded. Possible ways of doing this include being pushed in by another sprite, jumping fast enough, or wall running via a purple triangle.
Hitting a message box that isn't set to contain a message box will cause it to instead load the Yellow Switch Palace message. Ending the level via a goal tape or goal sphere will then make the game think the yellow switch was pressed. This is fixed by default by Lunar Magic.
For a brief period of time after hitting a flying ? block (even if it's been already "hit"), sprites can pass through it.
If Mario touches the bottom of a solid sprite while the sprite is either touching the top border of the visible screen from above or crossing it, he will be warped to its nearest side, with the same effects as the above. This glitch works even if the screen is scrolling.
As an exception to the above glitch, if a turnblock bridge is crossing the top of the visible screen and Mario's body is onscreen, he will not interact with the bottom or sides of the bridge rather than being warped to its side. In addition, if he is moving downward while touching the bridge, he will be warped on top of it; this effect can be used with vertically extending turnblock bridges to warp Mario upward, even through solid blocks.
If a turnblock bridge is touching (but not crossing) the top of the vertical screen border from below, Mario will not interact with the top or sides of it.
Turnblock bridges can push Mario into and through solid blocks if it expands while he is standing on it.
Activating the unused orange platform (sprite 5E) will also activate flying turnblock platforms. However, they'll move in the oppose direction that they're supposed to, and will horizontally move very slowly. If the flying turnblock platform is already activated when the unused orange platform is landed on, the turnblock platform will suddenly slow down horizontally.
When more than two flying turnblock platforms are activated at once, they don't always move in the directions Lunar Magic claims they'll go. The directions each platform will move in also varies depending on which platform you land on; sometimes they even all move in one direction, even if they're not meant to. The game even gets confused when reversing the directions of the platforms; they don't always change direction when they're supposed to.
Landing on multiple moving platform sprites at the same time will cause their effects on Mario's position to stack. This means if Mario lands on two platforms moving right, he'll slide across them to the right.
Any non-solid solid block will be overwritten when a tile-replacing sprite passes over it (e.g. vine, mushroom scale, growing/shrinking pipe, etc.). This includes ropes, ledges, and rotating turnblocks (however, the latter will return to a turnblock after its spin timer runs out).
When a vine sprite is spawned, it will always overwrite the block directly above it with a vine, even if it's a solid block.
The creating/eating block will immediately stop its path when another creating/eating block is spawned. It will resume movement when another brown block is touched.
If a block is hit and bounces as the creating/eating path block sprite is about to eat it, it will be skipped over without being eaten.
The eating path block sprite can skip over empty tiles without disappearing if there is a solid block in the tile to the right of it.
The eating path block sprite makes some unusual decisions when path finding. When given a choice of up or down, it will fly diagonally downward to the right at high speed. A choice between left and up/down will result in it going right (making it disappear unless the previous glitch is used). A choice between up, right, and down will send it downward, but will briefly accelerate as it changes direction. A choice of up, left, and right will move it slowly downward and to the right, before correcting itself and taking the right path. Finally, a choice of all four directions will send it flying diagonally upward to the right at a very high speed. Video
The eating path block sprite makes even unusual decisions when given the choice between paths on Layer 1 and Layer 2. Most setups will send the block flying in some direction.
If a block gets hit as an eating path block sprite passes over it, the block will respawn after the bounce sprite animation is finished, even though the path block should have deleted it. Notable in that it can cause the eating path sprite to backtrack.
Plantaporting: If there is a wall springboard at either y=12 or y=13, falling in a pit directly beneath it will warp Mario on top of it.
If a wall springboard is crossing the edge of the screen, its interaction will loop to the other side. In order for it to work, however, the base sphere of it has to be fully onscreen.
Mario can not be crushed by solid blocks while he is standing on a wall springboard. This can be used to drop him through solid blocks or through ceilings.
Similar to the plantaporting, if a Wiggler is placed at y=13 or any position above, Mario can bounce off of it by falling into a pit directly beneath.
Landing on a Wiggler as its head is turning on a corner can cause it to become stuck on the corner, or occasionally will fall off the edge. If it's on a ledge, it will always fall down.
Although Mario can not be killed by the segments of a falling Wiggler, each of them can still be jumped on.
Wigglers can't be killed by a Bob-omb being bumped into them, but will still turn around when touching one. This can be used to push a Wiggler off the edge of a ledge or into walls.
If a Wiggler gets pushed inside a block, it will either be pushed into the ground (if on top of a ledge) or shot 33 tiles into the air (if on top of a solid block), ignoring all solid tiles in the way.
Certain sprites will hurt Mario directly even if he's riding Yoshi, rather than knocking him off. These include Wigglers, Dino Rhino flames, Fishin Boo's flame, and Mega Moles.
If a sprite is on top of a growing/shrinking pipe as it is expanding, the sprite will end up stuck inside.
Killing a growing/shrinking pipe (by using a null sprite to mess with its properties) will cause it to act strangely; it will still try to act like normal and spawn pipe tiles, but it'll move horizontally at the same time. If Mario strays too far from it, it'll stop its normal functionality and fall off the bottom of the screen.
Mushroom scales and growing/shrinking pipes will overwrite any tiles they pass over, regardless of whether they are solid or not.
Mushroom scales will "lock" their position every 8 tiles.
Flying red coins can be burned.
Burning a Lakitu with a fireball rather than jumping on him will cause its cloud to never disappear.
Pressing both A and B at the same time while riding in a Lakitu cloud will cause Mario to spinjump out of it.
Pressing both up and down at the same time while in a Lakitu cloud will cause Mario to duck while moving upward. If you press up against a ceiling and then release down, Mario will get his head stuck in the ceiling and be pushed leftward.
Landing in a Lakitu cloud on the same frame that Mario would enter a wall far enough to walljump will push Mario inside and through the wall.
Lakitu's Cloud will not despawn offscreen, so it can loop across the level in any direction.
Since Lakitu and his cloud are separate sprites, having enough slots filled will cause only the Lakitu to spawn. Instead of flying around and throwing spinies, though, he'll just float in midair.
Cape-spinning a flying Lakitu will cause whatever sprite is in slot 9 to have its stun timer set to 31.
If Lakitu spawns without its cloud, killing it by jumping on top of it will cause whatever sprite is in slot 0 to have its stun timer set to 31. If Lakitu has already spawned previously in the level, it will instead stun whatever slot Lakitu's cloud was last in.
Mario can still collect the Fishin' Lakitu's 1-up while dying. Fix
The Mario proximity detection routine for sprites (e.g. for Thwomps, falling spikes, Yoshi eggs, etc) loop across the screen borders.
Thwomps will only interact with blocks that their left side touches.
When Thwomps hit a very steep slope, they shift slightly to the side.
Thwomps will lock their position every 16 tiles, preventing them from rising back up if they fall too far. Similarly, a Thwomp can get pushed up above its spawn position if it lands on a slope or a slightly offset Layer 2, which will cause it to rise up to the next lock position instead.
While rising back to their original position, Thwomps will ignore any blocks in the way.
Thwimps can jump through corners where two solid blocks touch diagonally.
If a Thwimp jumps into a wall, it will lodge itself into the side of the wall to land on it.
The Sumo Bro's lightning will continue falling even if the game is frozen by $9D. During a screen scroll, it will not interact with solid objects during that time either.
The Sumo Bro's lightning will infinitely loop vertically until they hit a block. Will takes some time to fall, though.
If the first division is filled, the flames from Sumo Bro's lightning will spawn in strange positions. If another sprite is then spawned, it may warp to the location of one of the flames.
The Sumo Bro's flames may occasionally borrow graphics from other onscreen sprites. In some cases this may even completely warp a sprite to the position of the flame. Fix
If a Sumo Bro walks off a ledge, it will fly in that direction until it lands on something. This can also lodge it into walls.
Touching one of the three-platform sprite on the frame it spawns (by scrolling the screen all the way over and sticking to the side of the screen) will cause Mario to be warped leftward. This will send him through solid blocks, as well as still leave him with the ability to jump. Videos
When touching a revolving brown platform without actually being on it, some timers will decrease twice as fast. These include $1490 (star power timer), $18AC (Yoshi swallow timer), $18AE (waiting to stick Yoshi's tongue out timer), and $151C (Yoshi's tongue extension distance).
Mario can pass through any solid blocks while riding a revolving brown platform, though he'll still be pushed left and killed if he ends up fully surrounded.
Jumping on a dolphin as it is rising quickly may cause Mario to fall through it. Though less useful, this can also occur with revolving brown platforms.
In certain levels, dolphins will treat the area offscreen above the level as water, which in turn causes them to jump infinitely upwards until they eventually loop and despawn at the bottom.
Once a dolphin touches lava, its timer to jump will be set. As soon as that timer runs out, the dolphin will perform the jump, even if it's no longer actually in water.
Skull rafts can travel through solid blocks, as they only acknowledge the tops of blocks.
If a skull raft encounters a left facing very steep slope, it will get stuck and become unable to progress. Running onto the raft in this state can potentially clip Mario through the slope, as well.
Torpedo Teds and Fishbones will still act like they're alive when killed; you can still be hurt by it or spinjump off of it. You can't kill it a second time, though, unless you have a star. Fix
The moving hole sprite will allow Mario to fall through any solid block as long as he is touching it, not just through the blocks it actually covers.
If Mario is pushed off of a moving rope mechanism by a block, the game will continue to think he is in front of the sprite and will let him grab onto and jump off of the rope as if it is still there. However, this effect will be broken if he passes in front of another rope sprite, unless he is holding an item. Fix
When climbing upward on a moving rope mechanism, Mario will not interact with the tops of blocks. This can be used to enter solid blocks when the mechanism moving downward or falling.
If you press up in front of a moving rope mechanism for a single frame or land on the ground while holding it, Mario will be "pulled" by the rope even though he isn't holding it. This can also be used to retain a spinjump when jumping off of the rope. Fix
Mario can be slightly offset while riding on a moving rope mechanism if he grabs on and holds the direction opposite to the direction the rope is in (though offsetting vertically without a block to assist Mario is only possible while big). This can let Mario fit in gaps that normally would not be possible while riding the rope.
Pressing left and right at the same time will cause the directional coins to, oddly, move upwards.
The directional coin sprite does not become solid if a P-switch is pressed, even though its graphics do. This can cause Mario to be crushed by the blocks it creates. Fix
The directional coin sprite will immediately terminate if the game is frozen (via $9D) on a frame it's set to generate a coin.
In Layer 2 and Layer 3 levels, the directional coin sprite will not stop when hitting Layer 1 tiles, and will instead just overwrite them. It will completely stop if they hit the top of a solid block, however, though it'll remain stuck there until the timer runs out.
Mario can bounce off of Rexes while walking up slopes, regardless of how steep the slope is.
The sea urchin sprites have a tendency to not work correctly with slopes, and occasionally will get stuck inside them, unable to move. The very steep slopes can also cause the urchins to start moving twice as fast as they normally do, and can sometimes cause them to move diagonally instead of in a straight direction.
Rip van Fish can force their way through the sides of blocks if they swim into it for long enough.
When flopping out of water, the standard fish sprites have a small chance of clipping inside a block upon hitting its side. This will cause the fish to either climb up the wall or clip straight through it.
All underwater enemies other than basic fish will still act as if they're in water even when they're not; the only difference is that they'll sink downward as they move around.
If a Whistling Chuck that wakes up fish is hit by a shell in a lower sprite slot on the frame he starts whistling, then he will summon Super Koopas as well. Video
When smashing through blocks, Chargin' Chucks will only check the bottom block of a wall; this means that the block on top will be broken, regardless of what type of block it actually is.
Hammer Bros will start throwing hammers while they are sinking in lava. Fix
Jumping Bowser statues and Ninjis are able to jump through solid blocks. Fix (Ninji)
You can prevent a Bowser statue's fireball from being fired by freezing the game (via $9D) during it's spawn frames.
If a normal Bowser Statue is hit from below, it'll start shooting fireballs.
Boo rings have two slots for their data, but the first slot of data will only be used by the first boo ring spawned; all others will use the second slot. Since two rings can be spawned at a time, this causes the data from any two rings spawned more than six tiles apart after the first one to overlap. This means, if they're rotating in the same direction, the resulting ring will move at double speed. If they're in opposite directions, it'll instead be completely motionless.
If a sprite is in slot #0 while a Boo ceiling generator is active, the game will warp the sprite around the level, as if it were one of the ghosts that make up the ceiling.
The reappearing Boo generator will only interact with Mario on the screen the ghosts actually because visible; this mean if you travel more than a screen before they disappear, he can swim straight through them.
The Big Boo Boss can be hurt by any carriable sprite, though for springboards it will only do so on the first frame it is released.
All large 64x64 sprites, such as Banzai Bills, Big Boos, green gas bubbles, and even Bowser, will lose interaction with Mario if they pass even a pixel past the left border of the level.
Mario can capespin or bounce certain sprites that shouldn't be able to be killed, such as grinders, Bob-omb explosions, and Bowser's bowling balls. Many of them will also have glitched graphics upon dying.
When entering a room of a level, sprites will spawn facing where Mario was when he exited in the previous room, causing them to move in different directions depending on where he was. Notably, this also applies to the "No Yoshi" entrance cutscenes. Fix
Each item memory bit covers an entire vertical column (or horizontal row in vertical levels) within a subscreen. This means that, if item memory is enabled, setting the bit for a block (e.g. a coin, 1-up block, Yoshi coin, etc.) will also affect all of the other blocks in the subscreen's column/row once the level is reloaded.
When a coin is collected and permanently erased from a level, reloading the room will replace the spot the coin filled with whatever block was placed "below" it in Z-order. The same occurs with Yoshi coins, and collecting all five of them will permanently erase the coins even if item memory is untracked.
If a Yoshi coin is placed across a screen border, collecting it will cause the coin to graphically glitch and give Mario either constant supply of lives or coins, with the level of effect varying based on his Y position within the coin. It will also erase the two tiles 14 blocks below it, looping to the next screen if necessary. Fix
Certain sprites, such as P-switches, will not sink in tileset-specific lava, instead landing on top of it as if it were a solid tiles. Fireballs are also included in this list, and will bounce across the top of the lava.
Sprites will not sink in sloped tileset-specific lava tiles. Fix
Under the right conditions, a room of a level will act like normal, but all the sprites in the room will act like they're in water. Video and more info
Oddly, Sunken Ghost Ship (level 018) is hardcoded to not reset the "boss beaten" flag. As a result, beating a boss in the level will cause a few strange effects in the next level Mario enters, so long as the overworld isn't reloaded in-between. One effect is that Mario will freeze in place after hitting a goal tape or sphere rather than doing a goal walk, as if a boss had beaten. A stranger effect, however, is that Yoshi will use incorrect animation frames and will behave particularly oddly. More info
Purple triangles will not work correctly in Layer 2 levels; while running sideways, Mario will not be given Layer 1 interaction, causing him to be warped straight downward. Shells may also not be flung correctly. They can work if Layer 1 and 2 overlap, however.
While wall running, Mario will ignore the standard function of whatever he is running up, so long as it is solid some of the time. This means he can run up munchers, any kind of ledge or slope, tile-set specific lava, noteblocks, and even other purple triangles. This effect also lasts for a frame after he reorients at the top, allowing him to jump normally. Additionally, he will also run through any blocks that aren't always solid on his way up the wall, including upside-down slopes, standard lava, and water.
Mario will "stick" to any platform sprites while running up walls via a purple triangle, slowing him down to the speed of the platform until it passes by. One notable use of this is that it even applies to the animation at the end of a wall where Mario reorients himself, but his horizontal speed will remain unaffected, which can cause him to clip into the tiles in the next column over. It should be noted that this works with the solid platform sprites as well, but only if Mario enters at a position where he doesn't get warped out of it.
If Mario starts trying to run up a purple triangle without a wall next to it, he will sometimes move upwards more than he should. If there's a solid block two tiles above the purple triangle, he can pass far enough into it such that jumping will send him straight through. Similarly, if there's a solid block one tile in front of the triangle, he can be pushed into that instead.
Dying in a bonus game will produce a glitched GAME OVER message. In addition, the next time Mario enters the level he came from, he will spawn at the midpoint.
Trying to take a screen exit in a Yoshi wings room will reset the room.
If you hit a goal tape in a Yoshi wings room and are given a bonus game, the game will reset the Yoshi wings room rather than sending you to the bonus game room or overworld. If you touch a goal tape again after this happens, the goal walk will be skipped and the room will be immediately reset.
During the goal walk, the screen freezes in place. If you scroll the screen left before the walk begins, Mario will end up running into the right-side screen barrier, stopping him earlier than normal. If screen exits are enabled, he'll end up even walking offscreen (and consequently exiting to the overworld) despite not technically being the edge of a level.
Mario can jump over the goal tape if he's high enough off the top of the screen for his Y position to loop.
Mario can jump off of a switch palace switch on the frame he lands on it. You can also extend the time Mario continues to move before freezing by hitting both the switch and a goal tape at the same time.
If Mario activates a switch palace switch but exits the level before the message appears (via dying or side exit), then the switch will count as being hit but the level's event will not be set (meaning you can reenter it).
Activating the end of a level in the intro level will reset the room upon fadeout.
Dying or hitting a goal point on the title screen will cause the game to reload the title screen level as an actual level, allowing you to play through it. Although doors will take you to other rooms still, "completing" this level with a goal point will simply loop it back. Fix (for death)
If Mario exits the title screen level via a side exit (be it in the recording or playable version), he'll spawn near [0,0] on the main overworld.
Hitting a message box or spawning the display message sprite in the title screen (be it in the recording or playable version) will take Mario to the main overworld near [0,8]. If it's hit while on the recorded title screen, it will also glitch the graphics temporarily.
Receiving the intro message from a message box rather than a display message sprite will place Mario at an incorrect tile of the main map. Luigi, however, will still spawn in the correct position. This effect will also occur if you take a screen exit from the intro.
Dying in the intro or title level will take away one of Mario's lives without giving him a game over; this can cause his life counter to decrease to 0 and loop around to glitched numbers. If Mario's life counter ever hits zero, though, completing the intro level will just return him to the title screen rather than taking him to the overworld.
If Mario enters a room with an incorrect FG initial position, he may be killed by the vertical screen borders.
Entering a room with Layer 2 horizontal scrolling set to "none" will cause it to inherit the Layer 2 X position from the previous room. Fix
The long sideways Layer 2 scroll sprite has some odd effects when used in horizontal levels. Placing it at Y=0 will cause it to act like a leftward conveyor. Y=1 to Y=3 will cause Mario to shake when standing on layer 2, and Y=4 will cause both Layer 1 and Mario to constantly shake. Y=5 and below will for the most part either crash or hardlock the game.
Any of the Layer 2 scroll sprites intended for vertical levels will kill Mario upon spawning if Mario isn't already spawning on the same screen they are.
Wrong warp: Taking a screen exit 256 times will reload the level from the overworld. The issue with this, however, is that the space of RAM meant for overworld data gets overwritten by level data during level load. This cause the game to try to loading the tile in the level data where the level would be in the overworld data as the translevel number to spawn Mario into. Not only does this potentially allow you to warp to any level in the game (even unused ones), it also can cause some strange effects, such the level getting used as a "no Yoshi" entrance in places not meant for one. It should be noted, however, that the "no Yoshi" entrance prevents a level from being warped to, as it will load the correct level after being run. Fix - Video - Diagram
When placed next to a screen border, both the screen exit on that screen and the one the door is touching can be accessed depending on Mario's position.
Screen exits are inherited from the previous sublevel, meaning that a door will send you to whatever the last loaded exit on a screen was; it only sends Mario to level 0 if no exit has been loaded yet. This means a room can technically have multiple screen exits on the same screen in vanilla SMW, depending on what level you enter the room from.
Layer 3 tide interaction with most floating platforms is broken and may cause them to float infinitely upward. Fix
Floating platforms only check for water touching their leftmost tile.
If a sprite has a spawn index of 65 or more (i.e. it's the 65th sprite from the left side of the level), then its "killed" status won't be reset when moving between sublevels. Hence, if you kill the 65th sprite in one room, the 65th sprite in any other room of that level will never spawn.
Stopping the title screen animation on the frame Mario touches a coin will let him keep that coin even after the game is actually started.
Useless
If Mario enters a room with an incorrect BG initial position, the background may glitch when scrolled too far down or up. Automatically fixed by Lunar Magic 1.70+. Alt. fix
If Mario enters a room too far to the right, the level will display past the screen borders for a bit before snapping back and glitching some of the Map16 graphics until they are reloaded. Fix
Collecting enough silver coins produced by a silver P-switch will start giving Mario glitched 5-up and coin score sprites. Fix (for 5-up)
Collecting enough 1-ups from hitting/bouncing off of enough enemies will eventually cause the point counter to loop back to 100 points. Fix
Bouncing off Wigglers enough will start giving Mario glitched score sprites. Video - Fix
Despawning the coin sprite from a coinblock before it spawns the score sprite will prevent the points from being added to Mario's score.
Freezing the game (via $9D) on the frame a Koopa shell turns into a normal Koopa will cause its graphics to glitch during Mario's shrinking animation.
Two shell-less Koopas can enter the same Koopa shell if timed correctly, but only the last one to enter before the Koopa emerges will actually have an effect on what spawns.
Bullet Bills make no sound when spawning directly into the level, even though Banzai Bills do. Fix
Message boxes will not display any letters in transparent levels.
If multiple flying ? blocks are active ($1564 is set) at the same time, then all of them except the one in the highest slot will briefly turn invisible.
If Mario is climbing downward while holding B, touching a wall springboard will cause the bounce sound to be repeatedly played despite Mario never actually bouncing off of it.
If there is an offscreen P-switch or key in slot 0, its graphics will "stick" to a Lakitu's cloud.
The net tiles cleared by the climbing net door will improperly update if the sprite is placed across a screen or subscreen border. However, this only affects VRAM and not the actual tiles, so their interaction isn't changed. This can also occur if the screen scrolls far enough before the sprite redraws the gate tiles, though with the same issue.
The lightest blue shade of the Magikoopa's palette is animated backwards for whatever reason. Fix
If a Wiggler is flashing, then killing it won't make it actually die until it stops flashing. The same glitch occurs if Yoshi tries to eat it the Wiggler while flashing.
The hitbox for the extended sprite flower spawned when Wiggler is first bounced on is severely and unusually disjointed from its actual graphic.
Mario can still land on a Wiggler even after dying. Fix
If a Spike Top walks off a ledge, it will get stuck moving in a circle.
Spike Tops are able to walk down a sloped ledge, though it will do so strangely. Moving up slopes works fine, though.
If a Spike Top is surrounded by four blocks, it will start to quickly spin in a circle.
The bottom half of the vertical jumping dolphins loops vertically every 16 blocks.
Clappin' Chucks will bounce strangely when on Layer 2 that is moving downward.
If the Sumo Bro's lightning tries to spawn fire over a screen barrier while Mario is dying, it may create glitched fire graphics on the opposite side of the screen.
Sprites graphics will not display at any Y-position occupied by six or more platform or turnblock-based sprites.
The three-platform sprite (E0) does not spawn correctly in vertical levels, and will still try to spawn as if it's a horizontal level. Fix
When sinking in lava, sprites will slide through objects when moving leftwards (they'll be stopped while going right). May be potentially useful when combined with Yoshi.
Sprites that don't have gravity applied to them (e.g. Banzai Bills, super Koopas, etc.) normally won't sink in lava; however, if they're killed and are falling offscreen, they are actually given gravity and will sink in lava. If this happens, the sprite will temporarily revert to its normal animation while continuing to move in its horizontal direction of movement (sometimes even speeding up), though Mario can still not interact with it.
Reflecting Podoboos will display a glitched graphic while sinking in lava. Fix
If you kill Reznor fast enough, a stray Reznor sprite will appear on the screen, sinking in non-existant lava.
Making a smoke cloud from a fireball in Reznor's room when $010F is set to 00 will cause part of one of the Reznor platforms to disappear for a frame.
Screen scrolling will cause Reznor's wheel to temporarily dislocate until the screen finishes moving.
Scrolling the screen on the frame Reznor spawns a fireball will cause him to duplicate that fireball into all of the remaining extended sprite slots. Not particularly useful, though it might prevent him from spawning another fireball for a bit.
Ludwig will not actually start fighting until Mario passes a certain point, so you can kill him with fireballs before he even attacks by just standing behind that point, scrolling Ludwig onscreen, and shooting away.
If you hit Ludwig during the flipping of his jump attack, he'll continue to be diagonal during his hit animation.
Morton, Roy, and Ludwig just force Mario downwards if touched while Mario is moving upwards, rather than directly hurting him. As such, you can survive inside the bosses so long as you jump often enough.
After hitting Roy, if you run against his walls as they move inward, Mario will to be pushed by them and will instead end up inside the wall.
Cape diving into Iggy/Lemmy's platform when it's rotated at it's near its maximum degrees leftwards will cause Mario to warp strangely on top of the platform, likely sending Mario either directly on top of Iggy's position and hurting him, or briefly sending him into the lava where he immediately dies.
The spots at the bottom of Wendy's bow "jump" when she animates, even though there's no logical reason for them to. Fix
Fireballs can cause some of the Bowser battle's blocks to briefly disappear if they're onscreen as Peach descends from Bowser's clown car.
If you grab a goal sphere in the Bowser fight and Peach spawns before Mario finishes the walk, the game will immediately fade to the overworld with the credits fade effect.
Mode 7 boss interaction loops between subscreens, allowing you to hit bosses that use it if you fly high enough.
Spawning a Koopa Kid that uses Mode 7 in a room where Mode 7 is already active will cause the room to glitch in unusual ways. Video
Most non-standard sprites types will loop their graphics over screen borders. Fix (smoke)
Destroying certain extended sprites with a star will cause their graphics to move slightly or have glitched graphics based on their orientation for a frame.
Freezing the game by eating a berry on the same frame that the bonus coin game cloud spawns a coin will cause it to spawn several of its remaining coins at once. Not especially useful, though, since they're counted as extended sprites and therefore won't cause most sprites to despawn, but it is a way of getting the cloud's coins to spawn earlier than normal.
Getting hurt will reset the bonus coin game cloud's collection counter, meaning taking any damage will make getting the 1-up impossible.
Having too many extended sprites onscreen can produce some strange graphics effects, particularly on Mario. A few examples of these are displacing his cape several tiles away or erasing parts of hit animations that don't fit into the standard graphical area.
Enemies killed so that they fall downward will still interact with very steep slopes on their way down. This glitch can be combined with the Torpedo Ted to get an interesting use out of it, though.
Pausing the game on the frame the game's music would normally change will cause it to continue playing the song (e.g. right before touching the goal tape)
Taking damage on the frame Mario enters a pipe will cause the shrinking animation to be skipped.
Dying on the frame Mario takes a screen exit will cause the next room's music to be replaced by the death theme. Can also be done in the intro level on the frame the message appears.
Dying in a level that has the time set to 0 will cause the game to display the TIME UP! message instead of simply fading to the overworld. Fix
Dying during the goal walk will glitch the circle effect and not count as completing the level.
Blocks or sprites that move Mario quickly (e.g. noteblocks) will cause the parts of the goal walk circle to not be redrawn as he moves.
Ending a level via goal tape offscreen will cause the circle effect to loop to the wrong screen, occasionally glitching overworld palettes as well. Fix
If Mario finishes a level while climbing, he will continue to climb during the goal walk, even during the thumbs-up pose.
In vertical levels, the goal tape will stop Mario as if it were a goal sphere, instead of activating the goal walk.
Hitting a goal tape after defeating a Koopa Kid will cause bonus stars to be added to the counter, but even if you pass 100, there won't be a bonus game.
Keys, throwblocks, and powerups (except 1-ups) will simply disappear when hitting the goal tape, instead of turning into a coin.
Ending a level via keyhole while offscreen may cause the game's palettes to glitch and the keyhole animation to loop.
The flashing color of Yoshi coins will not fade to black on level end.
If a Yoshi coin on Layer 2 is placed across a screen border on an odd-numbered screen, collecting it will cause some tiles in Layer 3's graphics to become corrupted (specifically the digits 0 to 7) depending on the x position within the screen where it is collected.
In addition to Yoshi coins, other multi-tile objects that change mess up over screen borders as well, including switch palace switches and fence gates. The former isn't particularly useful, however, and the latter only updates VRAM, not the actual tiles.
Scrolling the screen far enough to the right or left before flipping a fence gate will cause some of the tiles for the gate to appear on that edge of the screen. Unfortunately not useful since it is only the VRAM and not the actual tiles being updated.
Yoshi Wings may occasionally steal graphics from other sprites while flying offscreen, causing them to look like they're weirdly flying across the screen. Unfortunately, the interaction doesn't come along with it. Video
When sinking in lava, sprites will slide horizontally, even through solid blocks. Can actually be useful with Yoshi if he has a sprite on his tongue, though.
Crossing a screen border in a vertical level can cause pipe palettes to "split" between to colors. This can also happen in horizontal levels with vertically scrolling Layer 2 if it crosses over the vertical screen barier to the next screen.
The inside of the pipes used in the Lemmy and Wendy battles are non-solid.
Mario will not move with Layer 2 objects, resulting in him sliding across horizontally moving objects. The same occurs when climbing, as well; Mario won't move with the vine/net he's holding onto, which can also allow him to pass into and through solid layer 2 blocks if they're directly above the vine/net.
When the On/Off-switch-controlled Layer 2 sprite hits its lowest level, all sound effects that use $7E1DFC (including spinjumps, coins, and fireballs) will be replaced by the "smash" sound. Fix
When an autoscrolling level passes the screen limit for the level, its graphics (but not interaction) will loop.
If Mario finishes a level with more than 400 seconds left, the end-of-level score counter won't add correctly. Fix
If the timer goes above/is set above 999, then it will use hexadecimal numbers until it decreases below 999 again. Fix
If the exit counter goes above 99, additional numbers will be in hexadecimal. In vanilla SMW, this can only be done in the Japanese version; any other version stops counting when the star appears. Fix
Sprites other than standard powerup sprites will have glitched graphics when in the item box. Fix - More info
If you pause the game on the overworld while passing a jumping fish, the fish will repeatedly jump in place until you unpause.
Obtaining the secret exit in a level set to activate event 77 will cause garbage event data to be loaded on the overworld.
If an overworld sprite is placed in the Yoshi's Island or lower Donut Plains area on the main map, then the title screen will have some extra garbage tiles. Diagram - Fix
The S in the _____ START! message uses palette 8 instead of palette A like the other letters. Fix
Loading a level that has a "no Yoshi" entrance (by way of the 256 exit glitch or otherwise) when the entrance has already been run will prevent the cutscene from displaying, but will still function as normal, preventing both Yoshi and warps.
Loading a "no Yoshi" entrance from a pipe with the 256 exit glitch will cause Mario to not animate correctly. Additionally, bringing an item will cause it to stick to a bush during the walk, and bringing a Yoshi will cause the timing of Mario's movement to get offset due to him being unable to spinjump off, causing him to walk straight through the gate (though you don't keep Yoshi, unfortunately).
Collecting a star or dying on the title screen will cause the music to change to the special world's theme. Fix (for death)
Pressing a P-switch on the title screen will cause the music to disappear completely until the switch's timer runs out, after which it will be replaced by the main overworld music.

Locks and Crashes
Transforming into caped Mario while offscreen in an autoscrolling level will softlock the game. Fix
Screen scrolling an autoscroller sprite onto the screen will softlock the game.
Swallowing a berry on the same frame Mario collects a powerup or takes damage will softlock the game while giving Mario an infinite supply of coins. Fix
Swallowing a berry while dying will hardlock the game. Fix
Spawning a Podoboo without sprite buoyancy enabled will hardlock the game.
Transforming on the same frame that Mario does his victory pose at the end of a bonus game will hardlock the game.
Eating certain sprites via item swap may crash the game.
Spitting out a null sprite while on a brown revolving platform may cause the game to crash.
Collecting powerups with a powerup status greater than the fireflower may cause the game to crash.
Some stunned sprites may crash the game when attempting to spawn an invalid sprite.
Sending a directional coin sprite off the left side of a level with Layer 3 may crash the game.
Increasing the high bit of the mushroom scale sprite's Y position in a vertical level will crash the game.
Spawning more than one Big Boo Boss will cause the game to crash or, at the very least, noticeably glitch the screen.