Revenge!Sans is the RevengeSwap version of Underswap Sans. He does not believe the protagonist can do good, and instead, tries to kill them with puzzles, like Underfell Papyrus. He is the best friend of Revenge!Alphys and the younger brother of Revenge!Papyrus.
Revenge!Sans looks much like US!Sans, only with more red and black on his battle body and his scarf is more tattered. He has a big slash on his chest, where the protagonist killed him.
He is very kind and loving to Revenge!Papyrus, protecting him from the final blow from Chara in fighting, as he is aware of his 1 HP. He is aggressive to the protagonist, except in a True Pacifist Route.
"You hate us all that that much? Enough to kill us twice? Mwahaha... You'll regret this on your next run, kid. Mark my words..."
– After a completed Genocide Route
"I thought I believed in you... I guess even the Magnificent Sans cannot always be right..."
– Before his battle
"You spared everyone... Even those that didn't deserve your mercy... You did good..."
– After completed True Pacifist
(Note: Sans's True Pacifist quote is after Napstaton leaves)