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This is a list of glitches in the game Super Mario World 2: Yoshi's Island.
Glitches
NOTE: All names are conjectural unless otherwise specified.
Bowser Glitch
This glitch is hard to execute. When fighting the final boss, if Bowser gets close enough and breaks all the platforms, he flips and heads in reverse. He duplicates a lot of times, and returns later. This glitch has a somewhat extremely slow progression. Also, if all the platforms have been destroyed when Bowser is defeated, the game freezes due to Bowser not landing on a platform.[1]
Eating Baby Mario
NOTE: Yoshi must have the 10 Stars or 20 Stars item to activate this glitch.
In World 5-5: Goonie Rides!, the player should go to the area with the Helicopter Morph Bubble. The player should hit a Goonie and wait until the counter reaches zero. While the Toadies are taking Baby Mario away, the player should quickly hit him with Yoshi's tongue and touch the Helicopter Morph Bubble. Once Purple Yoshi has already transformed, the Toadies try to take Baby Mario again. When they pop Baby Mario's bubble, the player must open their inventory and select the 10 Stars or 20 stars item. When the Toadies are gone, the player must wait until Yoshi transforms back to normal. The player is able to eat Mario if Yoshi licks him. Even though Baby Mario is still missing, the game does not freeze, but the level is rendered impossible to complete.[2]
In World 2-7: Lakitu's Wall the player can do the same glitch, instead of turning Baby Mario into an egg hit the message box for baby mario to reappear in the air, do this two or three times and he should be able to hop back on Yoshi's back, however, his sprite animation while moving Yoshi is a bit unstable, the player can fix this by hopping on a transformation bubble. [3]
Glitchy Screen
Note: This glitch occurs on the console and not the game, and is not present on all SNES consoles.
This glitch occurs during specific areas where the graphics are rendered incorrectly. It seems to occur where translucent and transparent objects are. The screen becomes filled with various twitching objects, and Yoshi as well as all other enemies and objects disappear. Since the player cannot see anything but the terrain, this glitch makes the game nigh unplayable. The screen momentarily returns to normal when the game is paused, although it is only visible for a fraction of a second. This glitch appears to be a flaw in the SNES's rendering capabilities as opposed to the game's, as it only occurs on specific consoles and not specific cartridges.
Giant Yoshi Egg in other stages
Giant Yoshi Egg's cannot be carried into other stages as soon the player passes by the Goal Roulette, however, this can be bypassed by going into one of the stages that can make Giant Yoshi Eggs (World 2-1 for example). At the end of the level go to the far right of the Goal Roulette, jump and egg shot in the air and as soon the Giant Egg lands, tongue the egg and it should stand as far as it goes, next jump into the Goal Roulette and the next Yoshi should be able to pickup the egg and carry it into another level, like Huffin Puffin's chickens the egg becomes glitchy but can still function correctly.[4]
Message Block's Hidden Power
In World 2-7, Lakitu's Wall, Yoshi can eat a Fat Guy for a Giant Egg. When Yoshi arrives to the part with a Car Morph Bubble, he should hit the Message Block with the Giant Egg to make every thing freeze for a little while. When that is over, the stars from above will fall to the ground and Yoshi becomes invisible. Yoshi can still walk around while unseen. If Yoshi jumps through the goal roulette while invisible, the whole game freezes and the player must reset their Super Nintendo Entertainment System. In the Japanese version, the controller becomes unresponsive after the Message Block text appears, requiring a reset.
Nothing in Yoshi's Mouth
In places like World 3-1, there may be situations where it looks like Yoshi has something in his mouth, but he really doesn't. First, the player must have Yoshi eat a Grinder and keep it in his mouth until he reaches the checkpoint. Then, as soon as the player touches the ring, he must spit the Grinder out (the player must hold up while spitting it out). The Grinder that Yoshi spits out turns into a star, but before it even does that, the player can see that the spat out Grinder is invisible. When the checkpoint sequence ends, the star from the Grinder can be collected, but Yoshi also has an invisible object in his mouth. He can still stick his tongue out, but he can't eat enemies. When the player presses down with the invisible object still in Yoshi's mouth, he produces an invisible egg.
Yoshi's Tougue Glitch
Nothing in Yoshi's mouth glitch can be preformed in World 3-3, you can use either a giant egg or a POW powerup, after doing the glitch correctly, the player can use Yoshi's glitched state to break the game, get to the Stretch shy guy and defeat the small green shy guy, then turn and hold left and take damage with Yoshi's tougue sticking out, he will turn invisible and once he does grab baby mario and start fluttering to the right, now it's a race against time to reach the transformation bubble before the game crashes, this causes the stage to fall apart and failing to grab the transformation bubble crashes the game, by touching the bubble this can prevent the game from crashing and function somewhat normally, the stage is completely broken, this can be fixed by touching a save ring and purposely losing a life, as the result of using the glitch and beating the world 3 boss Navel Piranha, the cutscenes through the rest of the game are destroyed, all the sprites on Yoshi's Island gets placed randomly as the cutscene plays out, same thing applies to the ending cutscene.[5]
Warp Glitch
This glitch is possible in the SNES version. There are several levels where this glitch can be performed, and all of them rely on Yoshi entering a warp from multiple coordinates. In the Game Boy Advance version, Yoshi's Island: Super Mario Advance 3, it causes the game to freeze.
In 1-5: Burt The Bashful's Fort, Yellow Yoshi must go into the second room where the locked door is located and enter the pipe. Then face right and aim an egg shot wait a moment and hop backwards to be damaged by Piro Dangle. Once Baby Mario is floating and just about near Yoshi, keep fluttering up to the exit until you grab him, this will make Yoshi warp out the fortress and skipping the miniboss.
In 2-4: Bigger Boo's Fort, before Yellow Yoshi leaves the second section through the Warp Pipe, the player must let the lower Boo Blah go towards Yoshi and the pipe. When the Boo Blah meets the pipe, Yoshi must jump on it and enter the Warp Pipe at the same time. That way, Yellow Yoshi enters the pipe, but overhead. This causes the game to warp Yoshi out of the fortress.
In 3-1: Welcome To Monkey World!, when Green Yoshi meets the secret passage to the bonus area, he must simply jump in the water on the left overhead wall and dive in towards the left. Then, the player must press Pause before doing it, making sure to go towards the left and then quickly get back to the warp. If done correctly, Yoshi is warped out of the level.
In 4-7: Ride Like The Wind, Red Yoshi must have used the hidden Spring Ball towards the platform before the bonus area. Before Red Yoshi enters the bonus area, he must spring off the Spring Ball and touch the left wall at the same time. If done right, Red Yoshi touches the left wall and be warped out of the stage. Yoshi can also bring Huffin Puffin chicks into World 1-1, however if they are taken to another stage, their sprite becomes glitchy being some kind-of red cloud texture, but they are still functioning correctly.[6]
In 5-4: Sluggy The Unshaven's Fort, Yellow Yoshi must grab a Shy Guy in his mouth with some eggs in his stash. Once you reach the pipe get rid of the spikes on the floor to reveal a pit, stand to the left of the pipe and spit out the shy guy so he can land on the floor. Then step on the shy guy and fall to the pit and as soon Yoshi is off-screen, flutter to the left and to hopefully trigger the exit. This glitch is very difficult and precise to do so.
In each case, Yoshi is warped to coordinate (0, 0): the top-left corner of Make Eggs, Throw Eggs; he must then flutter around nine times while holding right on 
in order to reach solid ground. Clearing the stage causes the game to think that Yoshi had cleared the stage he had originally warped from, and the score he obtained upon completion carries over to the starting stage as well.
Zombie Yoshi
This glitch must be done in King Bowser's Castle, in Door 1. The player must go to an area where a ! Switch near a long lava pit can be found. The player would normally have to hit the switch in order to get across the lava, activating the Dotted Line Blocks. If the player jumps in the lava, in the direction of the switch, Yoshi performs a last jump, since he burned himself. If done right, Yoshi hits the switch, and comes back to life. The music stops, and the player controls Yoshi normally, even though he was supposed to lose a life. If the player attempts this glitch while Yoshi only has one life left, he has zero lives, as shown in the pause screen. However, if the player repeats this process, Yoshi instantly gets 999 lives.[7]
Airsickness
Attempting to use a melon's effects while riding a Lakitu's Cloud, at least on 5-1: BLIZZARD!!! where both watermelons and Lakitus occur naturally but may happen elsewhere with the use of items, causes Yoshi to use up all of the watermelon's effects uncontrolled. Yoshi spits out all watermelon seeds, and if he destroys the cloud while riding it with the red or blue watermelon, he uncontrollably spams his watermelon and then tongue afterwards, freezing the player in place until death or reset.
Blue Yoshi on World 6 Map
When the player arrives on the World 6 and get to at least 6-6, they can see Blue Yoshi, despite Green Yoshi being playable in the last level. The color is fixed upon reaching 6-8 or pressing right on the D-Pad to reset the Yoshi's positions.