"Once Upon a Time" is a chiptune song composed by Toby Fox for Undertale. It plays during the game's introduction sequence, which describes how the monsters were sealed underground after waging war against the human race, and shows the fallen human entering Mt. Ebott. It also briefly plays in the fake introduction sequence preceding the battle against Photoshop Flowey.
The track is one of the main defining songs of the game, and its melody is featured as a leitmotif in various other songs in the soundtrack, particularly ones used during important and emotional moments in the story, such as "Home", "Undertale", and tracks used in the fight against Asriel.
