Undertale is the 71st track in the Undertale Soundtrack. It plays while the protagonist travels throughout New Home and learns the backstory of Asgore, Toriel, Asriel, and the first human. It is a song harmonizing the melodies of Once Upon a Time and Memory/His Theme.
- In the game files, this song is split into two parts: "
mus_endarea_parta" and "
mus_endarea_partb." The beginning file loops while the protagonist is on the top floor of the house, and the second plays once when the protagonist enters the basement.
- The sound files play at 0.85x speed in-game, matching the speed found in the original soundtrack.
- This is the longest track in the Undertale Soundtrack, although its individual parts are shorter than Reunited.
- The original version of "Undertale" had a bit more somber feel and came with an entirely different guitar accompaniment. According to Toby, by hearing "Redline Day," he was inspired to rework the song and write a new guitar accompaniment, which would then become the basis for "Memory" (and, by extent, "His Theme").
- If a part of "Undertale" is slowed down by 666%, it sounds exactly like The Choice.