In fanart, they are often depicted with sharp teeth, and a lot of his AU selves have sharp teeth. What's interesting is that many of the monster characters have sharp teeth, but Sans and Papyrus do not in canon. He is part of the 'monster race' in Undertale. Sans has a much more detailed description on the Undertale Wiki. And there was disproportionate horniness for practically every Undertale character, but since Sans was the fan favorite, the thirst for him was almost beyond comprehension. Ultimate (as a Mii gunner costume, but you can fight as him nonetheless). The sheer drama of this boss battle made Sans the fan favorite, and he actually represented Undertale in Super Smash Bros. In this battle Sans has a very different attitude than the rest of the game and reveals incredible powers that you do not see in a normal playthrough. However, in a playthrough where you kill everything (a 'no mercy run'), Sans is the final boss and he is one of, if not the most difficult boss battle in the game. He comes off as too lazy to put up a fight. Throughout a normal or pacifist playthrough, he befriends the player, but unlike other characters who do this (except for Alphys) you do not fight him in a normal playthrough. He is the brother of another skeleton, Papyrus, who contrasts his character in many ways. Sans is a major character in Undertale and the first character the player meets outside of the Ruins. 2.6 Fanon Splintering and Self-Shipping.

Sans the skeleton sprite