- For the prologue of Undertale, see The War of Humans and Monsters.
"Once Upon a Time" is the 1st track in the Undertale Soundtrack. It plays during the introduction sequence of the game on every launch. It is the primary leitmotif of the game.
- This track plays at 90% speed in-game. In the original soundtrack, it plays at the same speed as it does in-game.
- This track is used two times in the game; the second is during the fight with the final boss of a Neutral Route after the boss closes the game. Upon relaunch, the track plays normally before leading to a fake version of the original intro before "glitching".
- This track is loosely based on the track Mother Earth from the first Mother game of the Mother Series.
|Undertale Demo Soundtrack|
|1 - 10|| Once Upon a Time • Menu • Your Best Friend • Fallen Down • Ruins|
Anticipation • Unnecessary Tension • Enemy Approaching • Ghost Fight • Determination
|11 - 16||Home • Heartache • End • Nyeh Heh Heh! • Home (Music Box) • Empty House|