Hopper

Hopper is an unused enemy for the game Super Mario 64, discovered in the files for the July 25th 2020 leak (alongside Motos). The enemy is purported to be a grasshopper, judging from the joint names for the model of it. The model for Hopper is supposed to be minuscule, akin to like the butterflies in the final game.

It is most likely that Hopper would hop around, given the name. No animations or behavior code for Hopper seems to exist, so this would be the theoretical behavior for the enemy. This means that the enemy was most likely scrapped shortly after its creation. Interactions between it and Mario are also unknown, given the circumstances above.

Theories/Speculation
Given the name of the enemy and its model's colors, it is most likely that Hopper was replaced with the Money Bag enemy. Money Bag's behavior matches somewhat with what Hopper could have behaved like; Money Bag would hop around and walk for a few seconds after four hops, after which it hops around again. It could also mean that Hopper was an earlier version of Money Bag.

It is also theorized that Hopper would've been an earlier version of the Crazy Box item, considering that the animation for the Crazy Box is called "hopperjump". This could be a connection between the two entities. It is also possible that judging from this, Hopper would have been a rideable character much like Yoshi.

Trivia

 * Hopper, Motos, and Blargg all were seemed to be scrapped from the final version of Super Mario 64 at the same time.