I feel like the Mushroom Island has been sort of forgotten about as a cool and rare place within worlds. While I don't think it needs a total revamp, we already have husks, drowned, and normal zombies, so it's a little redundant to make yet another type of zombie, I think it would be cool to expand on skeletons. Make a skeleton type mob for the mooshroom island. A Fungilton, or something along those lines. Make it like a skeleton in the way mooshrooms look like cows.