List of Super Mario World 2: Yoshi's Island glitches
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This is a list of glitches in the game Super Mario World 2: Yoshi's Island.
NOTE: All names are conjectural unless otherwise specified.
This glitch is hard to execute. When fighting the final boss, if Bowser gets close enough and breaks all the platforms, he will flip and head in reverse, and will duplicate a lot of times and will come back later. This glitch has a somewhat extremely slow progression. Also, if all the platforms have been destroyed when Bowser is defeated, the game will freeze due to Bowser not landing on a platform.
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 will 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 still missing, the game won't freeze, but the level is rendered impossible to complete.
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 will become filled with various twitching objects, and Yoshi as well as all other enemies and objects will disappear. Since the player cannot see anything but the terrain, this glitch makes the game nigh unplayable. The screen will momentarily return to normal when the game is paused, although it will only be 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.
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 will be invisible. Yoshi can still walk around while unseen but it will be difficult. If Yoshi jumps through the finish ring while invisible, the whole game freezes and the player will have to 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, ingest a Grinder and keep it in Yoshi's mouth until you reach the checkpoint. Then, as soon as the player touches the ring, spit the Grinder out (hold up while spitting it out). The Grinder that's spat out will turn 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. But when the player press down with the invisible object still in Yoshi's mouth, he will also produce an invisible egg.
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 2-4: Bigger Boo's Fort, before Yellow Yoshi leaves the second section through the Warp Pipe, 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 will enter the pipe, but overhead. This causes the game to warp Yoshi out of the fortress.
In 3-1: Welcome To Monkey World!, when Yoshi meets the secret passage to the bonus area, simply jump in the water on the left overhead wall and dive in towards the left. Then, press Pause before doing it, make sure to go towards the left and then quickly get back to the warp. If done correctly, Yoshi will be warped out of the level.
In 4-7: Ride Like The Wind, Red Yoshi must have used the hidden spring arrow towards the platform before the bonus area. Before Red Yoshi enters the bonus area, he must spring off the spring arrow and touch the left wall at the same time. If done right, Red Yoshi will touch the left wall and be warped out of the stage.
In each case, Yoshi will be 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 will cause the game to think that Yoshi had cleared the stage he had originally warped from, and the score he obtained upon completion will carry over to the starting stage as well.
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 will perform a last jump, since he burned himself. If done right, Yoshi will hit the switch, and come 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 1 life left, he will have 0 lives, as shown in the pause screen. However, if the player repeats this process, Yoshi will instantly get 999 lives. 
Attempting to use a melon's effects while riding a Lakitu's Cloud, at least on 5-1:BLIZZARD!!! where both melons and Lakitus occur naturally but may happen elsewhere with the use of items, will cause Yoshi to use up all of the melon's effects uncontrolled. Yoshi will spit out all melon seeds, and if he kills the Cloud while riding it with the fire or ice melon, he will uncontrollably spam his melon 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 will see Blue Yoshi despite Green Yoshi being playable in the last level. The color will be fixed upon reaching 6-8 or pressing right on the D-Pad to reset the Yoshi's positions.