List of Yoshi's New Island glitches
From the Super Mario Wiki
This is a list of glitches found exclusively in the game Yoshi's New Island.
NOTE: Unless otherwise noted, all names are conjectural.
Fall Through Platform
If Yoshi goes to Bouncy Beanstalk Walk and enters a pipe that infinite Shy Guys come out of, they have to jump to the right side or the left side along while touching the ceiling, Yoshi will fall through the platform.
Inside Smiley Blocks
This glitch is only found on Beware the Boo Brigade. If the player jumps when a smiley block is about to crush him, Yoshi will go inside the smiley blocks.
Fall Out of the Stage
The player must do the Inside Smiley Blocks glitch and jump while they're in. Yoshi will fall out of the stage.
In the Wall
If Yoshi goes to Beware the Boo Brigade and stands on an edge of a smiley block, sometimes he might go through the wall.
Defeat Big Beanie without having to Remove The Vines
If the player battles Big Beanie with 3 or more eggs, with the Golden Flutter Wings, and touches the giant spiky vine that is blocking Big Beanie, Yoshi will jump over it and be behind it, and the player does not have to remove the vines in order to defeat him properly. Yoshi just has to aim and throw 3 eggs at Big Beanie and then he will be defeated without having to bypass the vines.
Die and Defeat Boss at the Same Time
If the player has Flutter Wings or Gold Flutter Wings after defeating Big Beanie, he or she must flutter to the gap without touching the ground, and then the player will die and beat the boss at the same time.
Going Through Spikes
On the level See Poochy Run! while ducking under spikes, if the player has Yoshi stick out his tongue, he'll pass through the spikes for a short time.
Early Tap-Tap the Golden animation
If Yoshi gets to the right-hand side of Tap-Tap the Golden in Bowser's Castle Break-In in the narrow corridor he is encountered in, his walking animation is slightly different. It is more like that of Super Mario World 2: Yoshi's Island.