I like it! Making all those enemies control well and stay balanced must be a lot of work. Though, there is rarely any incentive to actually possess something different other than curiosity. Are there any interesting gameplay interactions between characters? I can see it work similar to warioland games.
What do you mean gameplay interactions? I haven't played the warioland games yet, I'd love to know what that entails. I see it as you having a choice of what moves you want, similar to how kirby can take different powersets. There will be incentives to at least try out everyone in the final game
There is an enemy that can make you fat, which will make you go slower and unable to jump, but you can break blocks under you. You can also turn into a spring after getting hit by another enemy. Things like that make enemies more interesting, and also allows you to solve puzzles or just move through the map. Paired with your concept it could add another layer of depth, but since you are going for simple platforming it would probably break the pacing instead.