Sans is a skeleton and a reccuring character in Undertale.
Sans shows up in Snowdin along with his brother Papyrus. When Papyrus captures Mario (and falls in love with him) Sans leaves the house telling them "not to make too many babies", as a joke. After Mario destroys the police and the Giant dancing Papyrus robot, Sans shows up saying, "What monster could have done this?". He complains to Papyrus for letting the "human" escape. Mario faces Sans at the end where they have a big fight, like in the original Undertale. In the end though, Mario pokes sans in his "sexy" eye, leaving him shaking on the ground in pain.