After multiple playthroughs of UNDERTALE done by various players, a few of them heading into DustTale timelines, the game is soon left behind and forgotten after boredom begins to set in. Until one day, a new player booted up the game. Sans saw this, and decided to take action. Since this is a DustTale take, you could probably guess how that goes. The AU has five main routes; Confession, Repentance, True Pacifist, Neutral, and No Mercy. Sans will appear to “help” the monsters in the Ruins, but kills them before the human has a chance to. According to which route you play, Sans will act differently. He’ll mostly be confused on why a player would suddenly become kind after experiencing hundreds of No Mercy loops in the True Pacifist Route of the AU, or go full murder-mode in No Mercy runs. Sans’ behavior is described as being rationally insane. Sans also gains the ability to make the player see hallucinations of monsters that have been killed, serving as a distraction while he’s off doing other stuff. In No Mercy or Routes where the human kills monsters, Sans doesn’t outright kill Papyrus, but he tears off his limbs and jaw, as he feels this is how his brother will be protected from the human. Sans also interferes in several battles, and overall makes the human’s life much more miserable by working with Undyne or Toriel or using his eye trickery ability to have zombified versions of Asgore and Flowey fight you in Necroptosis.