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Undertale Yellow

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Title Screen

Undertale Yellow

Developer: Team Undertale Yellow[1]
Publisher: Team Undertale Yellow[1]
Platform: Windows
Released internationally: December 9, 2023[2]

AreasIcon.png This game has unused areas.
CharacterIcon.png This game has unused playable characters.
CodeIcon.png This game has unused code.
EnemyIcon.png This game has unused enemies.
GraphicsIcon.png This game has unused graphics.
ItemsIcon.png This game has unused items.
Sgf2-unusedicon1.png This game has unused abilities.
MusicIcon.png This game has unused music.
SoundIcon.png This game has unused sounds.
TextIcon.png This game has unused text.
DebugIcon.png This game has debugging material.
LevelSelectIcon.png This game has a hidden level select.

ProtoIcon.png This game has a prototype article
PrereleaseIcon.png This game has a prerelease article

This article is about a fan-made game project.
Articles about fan games require explicit permission from administrators. This page was given permission by Rachel Mae.

Undertale Yellow is a fangame of Undertale where you play as the yellow SOUL, a rootin' tootin' cowboy named Clover.

To do:
  • Document the unused/leftover SOUL modes
  • Document the leftover battles and such from Undertale Customs
  • Sections probably warrant reordering
  • Demo leftovers? obj_genoflowey and unused flag global.flGenoCutscene, obj_credits, global.story
  • obj_background_el_bailador_test_2_yellow
Video journalists (or whatever it's called): Please consider looking at the UTY wiki too. FrostTheFrozenFox et al. has some discoveries there that we haven't covered (i.e. copied over) yet.


Read about prototype versions of this game that have been released or dumped.
Prototype Info
Read about prerelease information and/or media for this game.
Prerelease Info
Debugging Tools

Unused NPCs

There are 3 test NPCS in the game's code, meant to test interactions. One is of Testlet, the next is of Dalv, and the last one is of a now-deleted character.


An unused NPC that uses Martlet's sprites, presumably used to test cutscenes activated by interacting with an object. Upon interaction, it says the following dialogue (without portrait):

* Hello. This is MARTLET.
* Just kidding, I'm TESTLET.
* I'm here to show you
  how I can walk around.
* Watch and learn, kiddo!

[after arrived == 1, which appears to be impossible]

* I bet you can't walk
  like that, scrub.
* Testlet, out!

[changes animation to martlet_fly_away which is nonexistent]

[after action_sprite == 0, which again, appears to be impossible]
[Testlet gets removed, cutscene ends]

(Source: Original TCRF research)


An unused NPC that uses Dalv's sprites. It faces the left and walks to (300, 120) along the X axis, with walk speed set to 2 and animation speed set to 0.2, and avoids the player.

(Source: Original TCRF research)


An unused follower for testing, implemented very differently in comparison to the actually used followers.

It uses removed sprites named spr_rals_up, spr_rals_right, spr_rals_left, spr_rals_right; the name "rals" suggests that these sprites were of Ralsei from Deltarune.

(Source: Sophie (sophie.gay))

Unused Attacks


Bowll has an unused fourth attack, Bowll Test Song, which uses the Yellow Rhythm SOUL mode. As Bowll is immediately before El Bailador in the attack list, it was likely used to test El Bailador's attacks before the character was implemented.

This attack would've used the same patterns as El Bailador's attacks, but relevant script files, aside from a test script, no longer exist.

(Source: Undertale Yellow Wiki (FrostTheFrozenFox), original TCRF research)


obj_flowey_1_attack_shoebox obj_flowey_1_attack_audience

obj_flowey_1_attack_shoebox_creator and obj_flowey_1_attack_audience_creator are unused attack managers that are assumed to belong to Meta Flowey's 1st phase, due to following the same naming scheme as the standard attacks in it. They create and manage obj_flowey_1_attack_shoebox and obj_flowey_1_attack_audience respectfully.

  • obj_flowey_1_attack_shoebox is an attack where a basket dumps rows of 2 boots (with holes to slide by between the boots) constantly over the SOUL.
  • obj_flowey_1_attack_audience is an attack where an audience and a scoreboard appear, followed by the scoreboard lighting up the words "HATE", then the audience throws swarms of gravity-affected flowers at the battle box.
    • It would appear that "JOY" can also be displayed in place of "HATE"; in that case, mini-figures of the game's main cast will be thrown at the SOUL instead. However, it seems only related sprites remained in the game, instead of actual related code.

Neither attack has battle box dimensions associated, causing a game crash. The videos shown have their box dimensions set to 140 x 140.

(Source: Benjamin Urquhart (IAmAnIssue))

Unused Cutscenes

Test Cutscenes

Objects obj_cutscene, obj_cutscene2 and obj_cutscene3 contain cutscenes that appear to be for testing, with the last object already present in rm_debug.

However, obj_cutscene and obj_cutscene2 misuse cutscene_npc_walk in a way that causes them not to proceed correctly. obj_cutscene also doesn't initialize cutscene_music, causing it to crash the game by trying to play Blossom, and obj_cutscene2 doesn't end itself. obj_cutscene3 works as-is. The videos here were recorded from a mod that has those bugs fixed and puts each of those objects in rm_debug.

(Source: Original TCRF research)
To do:
Add some more elaboration/quality to the actions in the transcripts

[Starlo looks behind for a while then faces forward again]

* This is really bad.
* I'm a fake test Starlo.
* But I won't leave
  it this way!
* (It doesn't have to be this way.)

[Starlo walks a bit down]

[awkward pause]

[Blossom starts playing]

* A

[Blossom starts playing]

* I'm really sorry about
  the pops Starlo.
* When I see them...
  It's like a demon takes
* Look at it from
  my point of view.
* You're looking forward
  to some pops after a
  long hard work day...
* Only to come home
  just to see...
* Just to see...
* Argh!
* I need time...

[Starlo walks away to the left]

* Loool worth it.
* Those pops were

[Ceroba faces forward]

* What are YOU looking

[Blizzard Approaching starts playing]


obj_cutscene3 has Starlo walk into the player and initiate the fake battle cutscene with Rephil. It appears exactly as it does in-game:

[Starlo walks down for a bit, presumably to where the player is supposed to be]

[Fake fight with Rephil starts]

Whoa whoa whoa!
No need to start a
fight! Let's be
civil 'ere.
Do you attempt to
attack everyone you
Calm down, will ya?

[Game returns to the overworld, cutscene restarts]

Early Neutral Hotland Rooftop Cutscene

obj_hotland_roof_cutscene_neutral_2 appears to be an early copy of obj_hotland_roof_cutscene_neutral, without some details such as some dialogue variations and a quick-save before the fight with Meta Flowey.

Unused Dialogue

Unused Ceroba TALK line

Both of Ceroba's talk dialogues in the room immediately after meeting Axis is bugged. This is due to a break instruction being placed in the wrong spot, resulting in dialogue for the next room being pulled.

Intended Bugged
* So Axis is completely artificial intelligence?
* Well... artificial at least.
* Still, unemotional as he may be...
* The fact he so closely resembles life is impressive.
* Keep a move on, Clover.
* Well... artificial at least.
* Still, unemotional as he may be...
* The fact he so closely resembles life is impressive.
Intended Bugged
* Standing around won’t get us to Hotland.
* Come on.
* Keep a move on, Clover.
* Come on.
(Source: Undertale Yellow Wiki)

Unused Items

Various unused items exist in the game data.

Item Name Stat Info Info Text Use Text
Super Ammo 15ATK (Stated)
No effect (Actual)
* "Super Ammo" Weapon AT 15
* (Regular toy gun ammo sold
at your favorite convenience store.)
* (You load the Super Ammo.)
* (Your gun now feels lighter
than your conscience.)
Golden Scarf 25DEF * "Golden Scarf" Armor DF 25
* It's emitting a violently
golden shine.
* (You put the Golden Scarf on.
* Your tremendous taste for fashion
makes monsters go easy on you.)
Homemade Cookie Heals 20HP * "Homemade Cookie" Heals 20 HP
* (A little burnt on one side, but
looks yummy anyway.)
* (You scarf down the Homemade Cookie.)

Unused Rooms


An empty room. Based on its name, it appears to be related to GMLive in some way, similar to room_gms_debug_failsafe in Deltarune Chapter 1&2.

(Source: Undertale Yellow Save Editor)


Rm dunes 30 old nogrid.png

An older version of Oasis Valley, without the café and the fancy building leading to the mines.


Rm dunes 35 nogrid.png

Related to the previous entry; this room was supposed to lead to the café before it became a part of Oasis Valley.


Rm steamworks 07 nogrid.png

An old version of Steamwork's first steam vents section, containing a much harder version of it.


Rm steamworks 17b old nogrid.png

An old version of a room with a console that opens a gate in the Steamworks, lacking a section with steam vents.


Another empty room. Based on its name, it may have been used to inform playtesters of a build's ending at some point.

(Source: Undertale Yellow Save Editor)


Elementary, my dear Cactus.
This needs some investigation.
Discuss ideas and findings on the talk page.
Specifically: Since some GM update rooms can have children rooms (RPG Maker reference?), so maybe this has something to do with that.

An empty room that appears to serve as the base of the overworld portions of Meta Flowey's phase 1.

(Source: Undertale Yellow Save Editor)

Unused Summary Screens


rm_snowdin_14b_yellow rm_score_room
UTYellow rm snowdin 14b yellow.png UTYellow rm score room.png
UTYellow rm score room in-game.png

This slightly more crowded copy of the cabin of Honeydew Resort (rm_snowdin_14b_yellow) appears to have served as a roundup for a playtest build. As you can't move around, you can't see everything happening in it. You get to see some neat data, though.

  • COMPLETION TIME: In the format mm:ss
  • MARTLET CHASED OFF: Interestingly, the corresponding variable in this screen is named martlet_killed.
  • ENEMIES KILLED: As global.kill_number[0] is set to 9999, this number is normally ridiculous.
(Source: Undertale Yellow Save Editor, original TCRF research)


The screen (in the middle of fading out) as seen by changing the destination room of a Pacifist save

Another unused summary screen resides in a room named rm_summary. It shows the following data:

  • ROUTE: Pacifist/Neutral/Geno
  • FULL NAME: Hardcoded as Clover, or Gun-Hat if Flowey used that nickname in Snowdin
  • PLAYTIME: In the format hh:mm:ss
  • FUN LEVEL: Displayed as 420 instead if it's 100
  • SLRUPY SAVED: No.../Yes
  • BOSSES KILLED: Can contain Da (Dalv), De (Decibat), St (Starlo) and Ax (Axis), or simply be NONE
  • TIMES MO BROKE THE LAW: Random integer between 100-9000, with a 1/100 chance for another number between 1-100 to be added to it each frame
  • Additionally, "#breaktheshufflers" is drawn at y=340 (and invisible as a result).

A background that changes depending on the route the player was on would have faded in; however, the background sprites have been removed, and as the result only a pitch-white room will be shown, rendering the data illegible. 3.5 seconds after the fade in, the OST Kanako (or Greenhouse at 0.3x, if the player was on the Genocide route) will play, but will not loop.

Based on the mention of a "completion cards channel", this screen may have been made for a playtest build, and playtesters were meant to send a screenshot of this screen to the aforementioned channel.

(Source: Original TCRF research)

Unused Graphics

To do:
  • credits_resort
  • spr_battle_enemy_attack_el_bailador_light_cone
  • spr_attack_flowey_intermission_

Editor Sprites

UTYellow spr genoset.png

The sprite of the random encounter generator (obj_rndenc) is a winking face with a red right eye and a pink blush. Perhaps it's an evil cousin of Super Mario Bros. 2‍ '​s smiley.

(Source: Original TCRF research)


To do:
Apparently there is an unused variant of the scene that uses this.

Dalv has an unused animation for breaking the boards on The Dark Ruins exit during a Neutral run as the sprite name suggests, however, it doesn't appear at any point during the cutscene and instead just uses the pacifist version of the animation. This animation also exists in the demo but oddly was remade for Dalv's new design despite still not being used.


Sans' left-facing and up-facing walk cycles exist in the game data alongside three of his talk portraits.

These sprites are in fact part of the WildEast texture group; this means Sans was possibly meant to appear in the Wild East.

(Source: Undertale Yellow Wiki (FrostTheFrozenFox))


Ceroba has two talk portraits that go unused, it's unknown where they would have been used.


A version of Dina, the bartender in the Wild East, with a pink color pallet.


Just like Undertale, a room with coffins exist in the basement of the New Home. Normally, the player can only see 5 of the coffins, and 2 more being off camera. However, inside a game there exist a total of 8 coffin sprites (stored as frames in spr_coffins), with 3 of them being absent from normal gameplay: frame 2 containing a purple soul coffin, which is not present in the room at all, frame 6 being a duplicate of blue soul coffin (frame 4), and frame 7 being empty coffin without a colored heart and with no sign.


A full train sprite exists in the game and placed outside of the player's view in the Wild East.

Flowey Sprites

Two images of the Polygonal petal of Flowey's phase 2 glitching out. According to developer AeroArtwork, these were intended to show up during the phase randomly and sporadically, but were scrapped because they were found too distracting.

GameMaker Electricity Particle


A lightning particle texture from GameMaker's particle emitter presets.

Pre-Assembled Monster Battle Sprites

Assembled sprites of Ceroba, Dalv and Frostermit with some lines, possibly used to assist in aligning the separate parts of their sprites.

spr_ceroba_body_battle sprite678 sprite781
Spr ceroba body battle 0.png
Sprite678 0.png
Sprite781 0.png

Unused Zenith Martlet Frames

During the No Mercy route's final boss there is a section where Martlet takes off and very shortly returns to the battlebox as an actual obstacle that the player needs to dodge. Apparently the animation of her returning has some unused frames in which Martlet's colouring shifts from blue to white, telegraphing that she herself has became an attack. In the game, the first couple of frames are skipped entirely.

(Source: Original TCRF Research)


A random triangle and blob/stone. The triangle may be related to the light cones in the El Bailador battle, due to its similiarity to them.

Unused Enemies


Objects named obj_masterswordremix_body_a, obj_masterswordremix_sword_a, obj_masterswordremix_shield_a exist, appearing to be meant for a self-insert of developer MasterSwordRemix. obj_masterswordremix_body_a specifically seems to be based on an early version of obj_crispy_scroll_head_a. This in fact appears to be a removed enemy - there's no trace of associated sprites, dialogue, or other code.

Supposedly another self-insert of MasterSwordRemix, named Rodney, would appear as a part of the band in Honeydew Resort and UG Apartments' hotel.

(Source: Original TCRF research)

Unused Audio

Unused Music

There are a few unused tracks in the mus directory.


This track would have been played while reading through Dalv's diary entries; however, the game only tries to stop and not play it.


This track was likely intended for the Golden Coffee room in Snowdin. The final game uses "Fun-Sized" instead.


This track uses Martlet's leitmotifs; it might have been a precursor to Retribution, the theme of the second phase of her Genocide final boss fight.


"Enemy Approaching" from Undertale. There is a chance this was intended to replace prebattle1_yellow (which ended up becoming the normal Dark Ruins encounter theme) after the intro Froggit fight.

This is named mus_battle1 in the Demo and is referenced by two enemy objects, however there obj_radio handles battle music instead of enemy objects.

(Source: Original TCRF research)


"Shop" from Undertale. While gml_Object_obj_shop_generator_Create_0 defines it as the music of all shops except for the Wild West's gun shop, those shops and the gun shop's Genocide variant always inherit music from the overworld as hardcoded in scr_summon_shop.

(Source: Original TCRF research)


Attack segments of "DANZA", El Bailador's battle theme, with the orchestra hit notes. Aside from scr_audio_fade_out_battle and scr_audio_stop_sound referencing all of these probably by mistake, danza_attack_01_yellow is only referenced by test song data. Notably, some of the note patterns are slightly different from how it appears in-game.

(Source: Original TCRF research)

Early/Alternate Tracks

Unused Track Related Track
relaxation.ogg (Relaxation)
honeydew_lodge.ogg (Honeydew Cabin)
guardener_theme.ogg (TENTH LEVEL LOCKDOWN)
unforgiving.ogg (Duplicate)
mothers_love_phase_1.ogg (A Mother's Love)


cafe_arcade.ogg (unused) cafe.ogg ("Café Dune")

A chiptune version of "Café Dune". When the object obj_dunes_35b_dynamic_music is present in rm_dunes_35b, this plays when you approach the arcade machines in the room. There's also a chance this was originally intended for Mew Mew Love Blaster or another arcade game in the Oasis Café.

Duplicate Tracks


Duplicate of detainment.ogg (Detainment 014).


mus_gameover_yellow mus_justice

A version of gameover_yellow.ogg (Justice) with slight mixing differences. Interestingly, while the Demo's game over theme has the filename mus_justice, it (or at least the metadata) matches the final version.

Unused Sounds


This appears to be an alternate version of the jingle heard when interacting with a UGPS sign. For some reason, it takes Doki Doki Literature Club!‍ '​s theme leitmotif; perhaps this was a inside joke of the devs.

(Source: Original TCRF research)


Sans' talking sound from Undertale.


A weird, presumably dummied-out sound, supposed to be for Sans according to the filename. This is a duplicate of "House Guest" in v1.1 of the Demo.

Undertale Customs Leftovers

These appear to be artifacts of Undertale Customs, another Undertale fangame developed by Yellow programmer mysteryracer before joining the development team.

They are usually guarded under the condition global.game_mode == "customs".

Undertale Weapons Text

Undertale weapon info text can found in a unused object named obj_text_info_item_selection_pause_screen_overworld.

Weapon Info
Stick Weapon AT 0
* Its bark is worse than its bite.
Toy Knife Weapon AT 3
* Made of plastic. A rarity nowadays.
Tough Glove Weapon AT 5
* A worn pink leather glove. For five-fingered folk.
Torn Notebook Weapon AT 2
* Contains illegible scrawls. Increases INV by 6.
(After you get by an attack, you say invulnerable for longer.)
Burnt Pan Weapon AT 12
* Damage is rather inconsistent. Consumable items heal 4 more HP.
Empty Gun Weapon AT 15
* An antique revolver. It has no ammo. Must be used precisely, or damage will be low.
Worn Dagger Weapon AT 15
* Perfect for cutting plans and vines.
Real Knife Weapon AT 99
* Here we are!


Text related to a shop named Mart-2-Go from Customs was copied over to the Yellow game mode. There's no code to set up its items and song in gml_Object_obj_shop_generator_Create_0, and sprites for its background and shopkeeper no longer exist. The shopkeeper, the self-insert of mysteryracer in Customs, notes that you are not supposed to enter this shop upon entrance.

(Source: Original TCRF research)

Before buying something

  • Uhh... so how did you get here, anyway? [Upon entrance]


  • [Upon exiting]
    • Alright, catch you on the flip side!
    • Peace out!


Sprite Naming

A number of duplicate sprites exist in the file that don't follow usual sprite naming (spr_). Those include Toriel overworld sprites, her dialog faces, Frostermit sprite in his hidden and regular form, and 2 frames of Kanako's dialog sprite talking with her eyes closed.

Internal Music Names

While the internal names of music mostly reflect their names in the OST, some have notable differences.

OST Name Internal Name Notes
Seclusion coolestcave This song plays in the cavern in the Dark Ruins and used that name even in the demo version. With a name like that, one might expect this to play in an ice cavern, but the only two caverns in the game (ignoring the Underground) aren't ice-themed. The usage of "coolest" in this case is probably in the informal sense, then.
Mo Money gimme_ur_cash_yellow
Honeydew Cabin honeydew_lodge "lodge" is mostly the same term as "cabin", although "cabin" is more often used for houses in wild or remote areas, which is correct in regards to the location.
Sunnyside Farm sunnyside_ranch Also the same term-swap as Honeydew Cabin, as while "farm" and "ranch" are often considered to be interchangable, "ranch" actually refers to an area where animals are raised, which isn't very correct in regards to the location, which fits the definition of a "farm" more since the place only grows corn.
Tomorrow Means The Surface abandoned Correct in regards to the location (specifically, the intro to the Steamworks), likely just changed because the new title is more thematic.
The Freedom to be Flawed well_be_okay
just us missing_inaction All of the tracks relating to Flowey's neutral ending have lowercase, and very apt titles. It is possible that earlier in development, all of Flowey's tracks had longer, perhaps even properly capitalized names, and later on, the development team chose to rename the tracks to fit the more nightmarish themes of the ending, leaving just these track titles.

This one specifically seems to refer to the casualty classification.

subconscious the_wandering Ditto to "just us".
crescendo crescendo_of_dread Ditto to "just us".

Flowey Background

To do:
A whole section for stuff like this. IDK what to name that so...

UTYellow spr battle flowey final background.png

The background of the 1st phase of Flowey's boss battle has colors; however, it shows up distorted and in grayscale in-game.


  • All music in the game has a sample rate of 32kHz to presumably save space, except "Main Menu 5 (Steamworks)".
  • The following music are embedded in data.win for some reason:
    • Main Menu 5 (Steamworks) (mus_menu_steamworks)
    • AFTERLIFE (mus_f_phase2_gray)
    • Retribution (mus_retribution)
  • "AFTERLIFE" is also in mono for some reason.

Development URLs

Three URLs can be found in `data.win`, which lead to now removed pages, being Google Docs and Google Forms respectively. The other one would lead to a locally-hosted server.

Revisional Differences

To do:
Expand on what was changed. The original release note aimed to reduce spoilers.


The v1.1 patch was released on December 16, 2023, with the following changes.

(Source: Game Jolt)

Major Changes

  • Added two new accessibility options:
    • Easy mode: When enabled, the Hats now provide DEF values for an easier experience (can be changed mid-playthrough)
    • Auto-Rhythm: When enabled, automatically hits the notes in the El Bailador fight without having to press a button, if you are in the correct lane
  • Reworked the final pacifist boss fight attacks to be less chaotic and unpredictable
  • During the Axis chase sequence, Axis was supposed to slow down after every time he catches you. It now works as intended
  • Added an Act heal to the final No Mercy route boss (Also fixed a crash caused by this Act option being partially implemented but not working)

Crashes and Softlocks

  • Fixed a crash caused by using the “shoo” command twice during a dunebud duo fight
  • Fixed a crash caused by interacting with an object while completing the minecart puzzle
  • Fixed being able to backtrack on the second steam puzzle, which could lead to a crash and your save being ruined
  • Fixed a crash caused by pressing Z on frame 1 of the attack targetting cursor
  • Fixed a crash caused by a demo savegame being present on your system
  • Fixed a softlock caused by blocking Mo’s path as he leaves
  • Fixed a softlock caused by interacting with the crystal tree in Snowdin from the left
  • Fixed a softlock in the final pacifist boss fight where the selection soul would disappear from the menu
  • Fixed a softlock caused by sending one of the mine carts off-track
  • Fixed an issue that caused one of Cactony’s attacks to never end
  • Fixed a softlock caused by mashing through the text fast in the raft room in Snowdin
  • Fixed a softlock caused by turning around immediately upon entering one of the rooms in the late-game
  • Fixed a very specific bug that caused you to get stuck on a bridge upon retrying a fight under it
  • Fixed a crash during the Guardener fight that could happen on her last line of dialogue
  • Fixed an unrelated softlock in the Guardener fight
  • Fixed a crash on the final No Mercy boss caused by getting hit on the same frame as you defeat the boss


  • Fixed the tutorial buttons being swapped in the arcade minigame, also added additional information to the tutorial screen
  • Changed the Delta Rune Patch gold requirement from 150 to 100
  • Increased the item stock in the final shop of the No Mercy route (Applies on save reset)
  • Fixed mistakes in the credits
  • Fixed several line breaks, typos, and mistakes in the text
  • Altered one of Sir Slither’s act dialogues to make the sparing condition more apparent
  • Added an autosave after the final pacifist boss as a temporary help with reported performance issues in this cutscene
  • Added the Auto-Fire toggles to the death screen of relevant fights so you don’t need to restart the game and fights to change it
  • Fixed a mood-ruining issue in the final act, in which Chujin’s television would glitch out, blue screen, display an image of Chujin, and have blaring sounds during a cutscene; caused by a fun value of 60-62’s event occurring at an unintended time
  • Other minor fixes