fell Sans shows hatred towards humanity after they sealed monsters underground. Fell Sans, much like every other monster in Underfell, is a darker and edgier version of the original Sans. Sans can be harsh at times. And it takes a very long time for him to open up to people Fell Sans is very touch starved and due to how cruel the world is it’s not like he can admit it. He tends to hide how he truly feels with sarcasm or just plane rudeness.