HOW THE CRAP DOES ONE REMEMBER ALL THE UNDERTALE AUs??? These are the ones I remember (yes I'm just talking about sans):

Error Sans
Ink Sans (sorta)
Underswap Sans
Underfell Sans
And the one where the monsters are trapped in the moon instead.

probs more but don't remember. BUT THERE IS SO MANY MORE. LIKE, OMGG. STAHP.