Every monster when stunned: dizzy Clown gremlin (in boss fight) and Trigger teddies when stunned: *KABOOM* Hangry: OMG I'M BLIND (Smosh reference) Mama bear: what is life
Before anyone asks: Trigger Teddies aren't on this list because stunning them just causes them to explode. Probably best as they're an unending quantity of enemies (unlike Clown Gremlins who do indeed have a limit)
I wish the stun were their actual stand still animation. For example, the stun animation for the monkey is looking down, the actual stand still animation for the monkey is looking left and right