The goal walk will act as if Mario just beat a boss, causing him to stop moving upon touching the ground.
Yoshi will also glitch the frick out. His tongue can only spit out right (facing left will still stick it out to the right, only invisible). You also can't duck. There are a few different forms:

Square Yoshi -   Glitched graphic, with disjointed Mario. Tongue spawns 11 tiles below. Mario's hitbox is also somewhat odd, causing him to die if you're within 4 tiles of the bottom of the screen. With N Yoshis spawned, it occurs in the (40 % N)th highest Yoshi slot. If not on the main map, will be a lowrider instead

Lowrider Yoshi - Croutching graphic. Tongue spawns 10 tiles below. If one becomes visible offscreen, glitched graphics will display at the top of the screen. Occurs in the 7 slots below the square Yoshi's, looping lowest possible slot -> highest possible slot.

Chubby Yoshi -   Baby Yoshi graphic. Tongue spawns slightly to the left, causing the Yoshi to come in contact with anything its tongue pulls in before it's eaten. Wings do not appear from shells. Occurs for any Yoshis that aren't the other two.

Frozen Yoshi -   Normal Yoshi, but legs don't animate. Occurs for a Yoshi not spawned from an egg or Baby Yoshi.