"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."