Killer is one of many alternates of Sans. He works for Nightmare alongside with Dust, Horror, Raspberry, Cross, Red, Error, and you. 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 pimpricks, and a red target floats on front of his chest. A black substance similar to tears leaks out of his eye sockets. Besides Horror, Killer is your best friend..