Undertale Headcanons

Alphys and Undyne would match pajamas :"3

If they do not match the same pajamas, they will have the same theme (for example: with sanrio, My Melody and Kuromi)

sans makes and wears/sells cosplay. its the only thing hes not lazy about

Papyrus is a god 

Idk how common this theory/hc is anymore but I still love the idea that Sans and Papyrus are the last pieces of Gaster's existence in some way. It would explain how they just "showed up" in Snowdin and it would flesh out Gasters character a bit more, seeing as if they were like the core bits of his personality personified or something similar, then you would be able to see both sides to Gaster. my personal theory is that when he got scattered across space time, it sorta left him in the void with only his negative parts left, leaving them to fester. 

I have a LOT of theories for gaster <3