I figured out why his nickname is Forgot. Not because he's been forgotten by others, but because he forgot himself!
What if, after he killed Flowey, Papyrus suffered from so many negative emotions that he gained Generalized Dissociative Amnesia and completely forgot everything!?
(Yes, it's pretty dark. That's the point. I always wanted Forgot to be a very dark take on Papyrus. This is fricking perfect!)











