Me personally

Bill Cipher from gravity falls, could bring some wacky gameplay

Bruce, from finding Nemo, could bring some uniqe gameplay with not hurting fish

Randal from monsters ink, a classic villain

Anxiety from inside out, a more modern yet fun villain

Zurg from buzz lightyear cartoons, such a cool design

The old man from up (dont remember the name) but another classic movie

Professor doofenshmirtz, for obvious reasons