Killer is one of many alternates of Sans. He works for Nightmare alongside with Dust, Horror, Raspberry, Cross, Red and error His appearance is practically the same as the classic Sans the Skeleton, but instead, he carries a knife around him practically everywhere, he doesn't have the usual white pinpricks, and a red target floats on front of his chest. A black substance similar to tears leaks out of his eyes. Killer seemed to have a interest in you, ever since he saw you from the Corner