Leitmotifs

A leitmotif (/ˌlaɪtmoʊˈtiːf/) is a musical "phrase" or melody, re-used in multiple songs to associate a tune with a person, event, or place.

The extensive use of leitmotifs in Undertale ' s soundtrack and other sound files helps create a nostalgic mood for the game and often evokes emotional responses in players. Toby Fox has stated that the majority of Undertale ' s soundtrack was composed using reiterations of free SoundFonts and synths.

Attempts have been made at documenting all of the leitmotifs used in the game; players frequently find new connections, and it may be impossible to list them all conclusively. If somebody sends a post without any sources, it still needs to be analyzed before being deleted.

Timestamps found below are approximate to one second and are sourced from this playlist, which reflects the timing of the official soundtrack.

Once Upon a Time
This is one of the most frequently recurring melodies in the game. The original song can be divided into three sections, which together play in 17 songs.

"A" section

 * Once Upon a Time 0:00–0:28
 * Start Menu and Menu (Full)
 * The background tracks for the Start Menu build upon one another, with five intermediate tracks between Start Menu and Menu (Full).
 * The music played in the menu at the end of a True Pacifist playthrough is a slowed rendition of Start Menu.
 * Home and Home (Music Box) 0:36–1:11
 * Hotel 0:20–0:41
 * Can You Really Call This A Hotel, I Didn't Receive A Mint On My Pillow Or Anything 0:14–0:30
 * Undertale 0:37–2:49, 3:27–4:43, 5:20–5:58
 * The Choice
 * Fallen Down (Reprise) 1:18–1:44
 * Hopes and Dreams 0:00–0:44
 * SAVE the World 0:00–0:20, 1:46–1:53
 * Reunited 0:43–1:43
 * Bring It In, Guys! 3:27–3:35, 3:47–4:05
 * Last Goodbye 0:23–0:27, 0:45–0:48, 0:56–1:02, 1:40–1:42, 1:52–2:02
 * Good Night

"B" section

 * Once Upon a Time 0:28–0:58
 * Home and Home (Music Box) 1:11–1:45
 * Hotel 0:41–1:22
 * Can You Really Call This A Hotel... 0:30–0:57
 * Undertale 2:49–3:27
 * Fallen Down (Reprise) 1:44–2:10
 * Reunited 1:43–2:42
 * Last Goodbye 0:02–0:21, 1:08–1:29

"C" section

 * Once Upon a Time 0:58–1:29
 * Fallen Down (Reprise) 2:10–2:30
 * Hopes and Dreams 0:44–1:29, 1:52–2:15
 * SAVE the World 0:42–1:46
 * Final Power
 * Reunited 2:56–3:56
 * Menu (Full) 0:21 - 0:32
 * Last Goodbye 0:45–1:08

Your Best Friend
This leitmotif occurs in at least nine songs, as well as in at least one other sound file within the game and one sound test file.
 * Your Best Friend
 * Your Best Nightmare 0:54–1:26, 2:00–2:27, 3:00–3:27
 * Finale 0:00–0:40, 0:57–1:52
 * Hopes and Dreams 1:29–1:52
 * SAVE the World 0:04–0:07 repeating
 * Last Goodbye 0:29–0:32 repeating
 * mus_toomuch (this plays after exhausting the random kill counter of an area)
 * mus_f_finale_1

You Idiot

 * You Idiot
 * Your Best Nightmare 0:00–0:15, 0:22–0:46, 2:29–2:49, 3:28–3:51
 * Premonition (debatable)
 * Burn in Despair!
 * mus_f_part3

Fallen Down

 * Fallen Down
 * Empty House
 * Fallen Down (Reprise) 0:00–1:18
 * Respite 0:00-0:35
 * Bring It In, Guys! 3:35–3:45

The track Fallen Down in-game is played 25 cents above C# major in A440 equal-tempered tuning. The sheet music shown above is written in D major.

Heartache

 * Heartache 0:00–0:50
 * ASGORE 0:34–1:49, syncopated to 4/4

Ruins
Ruins is another common melody, appearing in at least 13 official songs and an unused sound file.
 * Ruins
 * Waterfall 0:27–1:49
 * Quiet Water 0:05–0:32
 * NGAHHH!! 0:34–1:22
 * Spear of Justice 0:36–1:52
 * An Ending
 * Don't Give Up
 * Reunited 0:00-1:43, syncopated to 4/4
 * Respite 0:35–1:54
 * Bring It In, Guys! 1:48–2:08
 * Battle Against a True Hero 0:44-1:35 syncopated to 4/4
 * mus_ruinspiano

Anticipation

 * Anticipation (identical percussion track, but no melody)
 * This song also plays at extremely reduced speeds when battling Monster Kid, during the final encounters with Flowey in New Home, and at the end of a "Soulless" Pacifist playthrough. (This version is sometimes referred to by fans as "In My Way")
 * Enemy Approaching 0:00–0:10
 * Stronger Monsters 0:00–0:32, 0:38–1:00
 * Bring It In, Guys! 0:00–0:10

Enemy Approaching

 * Enemy Approaching (melody)
 * Heartache 0:54-0:58, 1:00-1:01, 1:12-1:15
 * Dogsong (has the variation of the melody)
 * A slowed version of this song plays after meeting Endogeny's sparing conditions.
 * Temmie Village 0:11–0:16 repeating, also has the variation
 * Tem Shop, also has the variation
 * Stronger Monsters 0:00–0:32, 0:38–1:03
 * Bring It In, Guys! 0:00–0:40
 * Dogtroid 0:07-0:34

Ghost Fight

 * Ghost Fight
 * Dummy!
 * Pathetic House
 * Spider Dance

Bassline

 * Ghost Fight 0:08–0:16
 * Dogbass
 * Dummy! 0:07–0:21

Sans
Found in four songs, one of which is never played in the game. One version can be affected by a non-Neutral Route.
 * sans.
 * It's Raining Somewhere Else 0:19–1:18, 2:00–2:39
 * This song is most similar to the B section (0:10-0:17) of Song That Might Play When You Fight Sans.
 * This song is played slightly slower in Sans's Room.
 * Song That Might Play When You Fight Sans 0:01–0:33 (melody), 0:01–0:58 (bassline)
 * Bring It In, Guys! 0:43–0:46 (melody)

Papyrus

 * Nyeh Heh Heh!
 * Bonetrousle
 * This song is played at an extremely reduced speed when encountering Papyrus for the last time in the Genocide Route.
 * Song That Might Play When You Fight Sans 0:33–0:58
 * Bring It In, Guys! 0:35–0:44, 0:46–0:53

Snowy

 * Snowy 0:00–1:02
 * This song plays when fighting Snowdrake's Mother. It is heavily distorted, changing pitch and speed randomly every few seconds.
 * Snowdin Town 0:19–0:56
 * Shop 0:00–0:25
 * Dating Start! 0:00–0:35, 0:37–0:54 somewhat syncopated.
 * Dating Fight! 0:00–0:13
 * Bring It In, Guys! 0:54–1:17

Snowdin Town

 * Snowdin Town 0:56–1:10
 * Shop 0:25–0:50
 * Dating Start! 0:16–0:35, 0:54–1:31 somewhat syncopated.
 * Dating Fight! 0:13–0:35
 * Confession
 * Hopes and Dreams 2:15–3:01
 * Reunited 3:56–4:25
 * Bring It In, Guys! 1:17–1:29

Undyne

 * Dating Tense! 0:17–0:25
 * Undyne
 * Run!
 * NGAHHH!! 0:00–0:34, syncopated
 * Spear of Justice 0:00–0:36
 * Bring It In, Guys! 1:30–1:48
 * ASGORE 2:29-2:35

Asriel

 * Memory
 * Undertale 0:00–2:47, 3:27–6:21
 * At times, the melody is barely perceptible among overlapping music. It is heard on a guitar for most of the song, becoming hard to distinguish after 3:27. The tune switches to a more audible sample after 4:42, to a quiet background piano at the key change around 5:20, and back to the second SoundFont at 5:57.
 * The Choice (imperceptible), as it is a part of Undertale which contains the barely-audible Memory
 * Finale 0:40–0:57
 * His Theme

"A" section

 * Alphys 0:08–1:00
 * Bird That Carries You Over A Disproportionately Small Gap 0:06–0:13
 * Here We Are, syncopated to 5/4

"B" section

 * Alphys 1:00–1:25
 * She's Playing Piano
 * Here We Are 1:28 - 1:50
 * But the Earth Refused to Die

Area Bells
The theme originates from the piano ostinato from Ruins.
 * Waterfall 0:00-0:27
 * Another Medium 0:00–0:51 and 1:50–2:22 (synthesia), 1:36-1:50 (piano)
 * CORE 0:06–1:01, 1:29–2:10
 * Death by Glamour 0:25–0:38
 * Bring It In, Guys! 2:33–2:44

CORE

 * CORE 0:00-0:19, 0-20-1:01, 1:29-2:10, 2;37-2:46
 * Death by Glamour 0:00-1:04, 1:56-2:12
 * Bring It In, Guys! 2:15-2:44

"A" section

 * Another Medium 0:51–1:21, 1:50–2:14
 * CORE 0:34–1:01, 1:42–2:10
 * Bring It In, Guys! 2:44–3:07

"B" section

 * Another Medium 0:22-0:36, 1:21-2:05
 * CORE 1:01-1:29, 2:10-2:37
 * Bring It In, Guys! 3:07-3:26

Background

 * Another Medium 0:36-0:51, 1:21-2:05
 * CORE 1:01-1:29, 2:10-2:37
 * Death by Glamour 0:38-1:04 (played as a distorted motif)
 * Bring It In, Guys! 3:07-3:21

Showtime
Found in four songs and at least one other sound file.
 * It's Showtime!
 * Metal Crusher 0:04-0:19, 0:37-0:53
 * Live Report
 * Death Report
 * Death by Glamour 1:30–1:56
 * mus_tv (i.e., Papyrus's TV)

Bassline

 * It's Showtime!
 * Hotel 0:09-1:27
 * Can You Really Call This A Hotel... 0:07-1:01

Hotel
Hotel-related songs are largely part of the Once Upon a Time leitmotifs.
 * Hotel 0:00–0:20
 * Can You Really Call This A Hotel... 0:00–0:15
 * CORE Approach

Metal Crusher

 * Metal Crusher 0:20-0:37
 * Last Episode!
 * Death by Glamour 1:04–1:30
 * grandpasemi

Musical

 * Oh! One True Love
 * Oh! Dungeon
 * For The Fans

Oh My Leg

 * Oh My...
 * Death by Glamour 0:13-0:26
 * Bring It In, Guys! 2:21-2:33

Bergentrückung
Asgore's main theme is uncommon, appearing in only 4 tracks.
 * Bergentrückung
 * Undertale 5:11-5:15
 * ASGORE 0:00–0:35, 1:25–1:32
 * Bring It In, Guys! 3:28–3:34

Determination

 * Determination
 * This song is sped up, looped, and played over itself, as Flowey laughs at the protagonist for dying to him.
 * Alphys 0:31–0:59 (debatable)
 * ASGORE 1:50–2:28
 * Battle Against a True Hero 1:35-2:34 (debatable)
 * mus_snoresymphony
 * mus_kingdescription

W.D. Gaster
Gaster's Theme is a song that only plays in the Sound Test room. The Sound Test room, in turn, is only found half the time between rooms 46 (room_tundra_3, Snowdin – Box Road) and 47 (room_tundra_3A), and only when fun = 65.

Four-tone accompaniments are fairly common; any of the following could be coincidental, making all of them speculative.
 * Snowdin Town 0:19-0:20 repeating
 * Shop 0:04-0:06 repeating
 * Dating Start! 0:02–0:03 repeating
 * Metal Crusher 0:04-1:02
 * Song That Might Play When You Fight Sans 0:10-0:17 0:26-0:33
 * Bring It In, Guys! 0:54-1:28

Minor Differences between songs

 * The Joystick Config songs – Uwa!! So Temperate♫, ...Holiday♫, and ...HEATS!!♫ – are all variations of each other.
 * Spookwave to Spooktune
 * Ghouliday to Jingle Bells
 * Sample used in Barrier is used in Amalgam
 * Sample used in Ooo is used in Waterfall (0:14 - 0:25)
 * Battle Against a True Hero 0:00–1:36 to Power of "NEO"
 * mus_smile is Muffet's laugh, sped up, reversed, and looped.
 * Multiple songs from the soundtrack use instrument samples from other games.

MEGALOVANIA
This song is part of a unique leitmotif. The melody of MEGALOVANIA is not heavily recycled inside the game; instead, this leitmotif crosses between games, appearing most notably in Toby Fox's own Earthbound Halloween Hack, the seven-year webcomic Homestuck, and in the Mother fangame Cognitive Dissonance. The song's use as a leitmotif is associated with an endgame event or boss battle, bringing a familiar sense of finality and the absolute to the games in which it is used.