In the prototype version of Yoshi's Island, Yoshi is able to eat destructible walls (one tile at a time), and in fact does so automatically when approaching them. In the finished game, these can only be destroyed with other methods like projectiles, jumping into them from below, Ground Pounding, etc.; Yoshi can no longer eat them.

Super Mario Odyssey contains unused code for a "CeilingKeep" state for Mario that does not resemble anything found in the finished game, or in Mario games in general, which can only be described as "ceiling with ice floor puzzle mechanics".

A typical ice floor puzzle in a video game will take away the player's control upon stepping on a slippery surface and make characters keep moving in a straight line until they either leave the ice floor or hit an obstacle.

This state confers the same ability, bafflingly, to a ceiling instead. The ceiling would "grab hold" of Mario, make him move without player input in the direction he was facing when he touched it, and only let go when he reached the end of the ceiling.

What this could have been used for, and what such a ceiling could have looked like, is unknown.

Top: a diagram of the state. Bottom: an example of an ice puzzle, the Ice Path in the Generation II Pokémon series games.