Sans is the skeleton boss fought at the end of Undertale's genocide route, a 2015 role-playing game by Toby Fox, and his battle theme Megalovania has become one of gaming's most recognisable tracks. The second phase refers to the later, harder stretch of that fight, when Sans uses faster, denser attacks and the music pushes the tension higher. Clips of this section spread through gameplay videos, edits and soundboards, where fans reuse it as shorthand for an unfair or final boss encounter, keeping it popular long after the game's release.