dust sans is the brother of papyrus. To stop the human from killing everyone over and over, Sans is forced to increase his own LV. Killing one monster isn't enough EXP for him to defeat the child, though, and oddly enough, the resets don't send him back to LV one. He forgets his original purpose and kills everyone, including Papyrus. He begins to hallucinate a much meaner Papyrus who's just a floating head and hands. Sans can also locate SAVE points and destroy them.