Undertale Last Breath is a fan-made alternate take on Undertale, the 2015 role-playing game created by Toby Fox, focusing on a far more relentless version of the Sans battle. In the original, Sans is the final challenge of the Genocide route, and Last Breath extends that fight with extra phases and stronger attacks. Clips from these phases spread through YouTube playthroughs, fan animations and soundboards, where the final attack moment became a shorthand for an overwhelming boss move.