In Undertale, there are secret music files. To listen to the music files, click on the secret soundtrack link below. This page will help you learn about them. Secret Soundtrack
Sound Test Songs[]
Happy Town[]
Happy Town is a short cheerful jingle with the filename mus_happytown
Meat Factory[]
A short robotic track with the filename "mus_st_meatfactory".
Trouble Dingle[]
A short series of seemingly random robotic noises with the filename "mus_st_troubledingle".
Gaster's Theme[]
Upon selecting this track, no other songs can be selected. After listening to Gaster's Theme for a period, the room will cease playing music and display a screen that says "Thanks for your feedback! Be seeing you soon!". The protagonist is then returned to the room with the fishing pole. The file is titled "mus_st_him".
Miscellaneous[]
abc_123_a[]
Hello. He-he-he-he-have some respect and don't spoil the game.It's impossible to have mysteries nowadays,because of nosy people like you. Please keep all of this between us.If you post it online, I won't make any more secrets.No one will be impressed.It will be your faaaaault.
He-he-he-he-ha-he-he-ha-he-he.
-the Original abc_123_a file.
This sound file contains seven text-to-speech voices from the FL Studio 11 synthesizer telling the listener not to post the game's secrets online. The odd filename was chosen to force it at the top of an alphabetical file listing and make its presence more obvious considering that all the other .ogg-format music and sound effect files present in the executable are prefixed with either "mus_" or "snd_".
mus_smile[]
This track only plays in room_gaster, a room containing the 17th entry related to one of W. D. Gaster's experiments and only accessible through save file editing or debug mode. While it may not seem like there is much to it other than sounding distorted, it can be sped up by 1000% and have its pitch doubled to reveal Muffet's laugh, then reversed and looped.
grandpasemi[]
This audio file was originally found in the Undertale Demo as "grandpasemi.ogg" and is reminiscent of the intro to "Metal Crusher". As of Undertale v1.001, this audio file has returned as "grandpatemi" in the form of a sound effect and plays when refusing to give Temmie the Temmie Flakes.
Grandpa Semi was a cut character that may have been planned to be the grandfather of Papyrus and Sans which stems from knowing that Semi refers to Semi Serif fonts. The Korean version of the Undertale Demo, which is based on an earlier build of the English Undertale Demo, also contains evidence suggesting that the phone call that the protagonist receives in Snowdin Forest from Alphys was planned to be used for Grandpa Semi instead. It is unknown if this character was cut for W. D. Gaster during development.
mus_kingdescription[]
A regal-sounding variation of "Determination".
mus_dance_of_dog[]
This song plays in an error room containing a dancing Annoying Dog. This error room can be accessed by modifying the SAVE file. The speed of the song varies.
mus_sigh_of_dog[]
This song plays in an error room containing a sleeping Annoying Dog. This error room can be accessed by modifying the SAVE file.
mus_star[]
This song uses instruments from the SNES game, Star Fox. This is similar to Dogsong, which used instruments from a different SNES game called Mario Paint.
mus_f_part3[]
An unused third part of "Your Best Nightmare" which includes the alarm sound effect. This part of the track does not actually play and was scrapped in favor of reusing "mus_f_part1", "mus_f_part2", "mus_repeat_1" and "mus_repeat_2". This may be to make the fight shorter or maybe there were plans to include a fourth section to the Flowey boss fight, but only the song was implemented. Interestingly, in the OST version, "Your Best Nightmare" repeats the first part at the end.
mus_f_finale_1[]
An unused first part of "Finale". This track is never played, as "mus_f_finale_1_l" plays instead. It is simply a shorter version of the first part of Finale, most likely intended for when the player restarts their game after dying in the 2nd part of the Photoshop Flowey boss battle. "mus_f_finale_1_l" is most likely just "mus_f_finale_1" with the l standing for longer.
mus_piano[]
This song is simply "Good Night" in the Undertale Soundtrack and only plays during the ending screen of the Undertale Demo but not in the full version of Undertale.
mus_ruinspiano[]
This song is a slower version of "Ruins" with a variation on the melody.
Outside the game files[]
Alphys Lab (Unused)[]
An early version of Alphys's Lab that was left unfinished since it sounded too similar to a lab song from another game. It was replaced with "Alphys" in the final version.
Undyne Battle (Unused)[]
An early version of Undyne's battle theme before her personality was fleshed out. It was replaced with "Spear of Justice" since it didn't feel like Undyne was "heroically punching [the listener] in the face."
Dog Hole (Unused)[]
An unused track which was scrapped during development and was later uploaded to the official Tumblr.
Dogtroid (Unused)[]
Allegedly, this track would have played upon beating the game fast enough. Once this happened, the Annoying Dog would appear in a bikini, which is a reference to the Metroid series.
Undertale (Unused)[]
An unused iteration of "Undertale" which was said to be more melancholic and less effective. This iteration was scrapped when "Redline Day" from the anime film, Redline inspired Toby Fox to change the chords and guitar accompaniment, which would then serve as the basis for "Memory".
Patient[]
Patient was an unfinished song for Homestuck that used the "Doctor" leitmotif. The song would later be reworked as "Another Medium" for Undertale.