Fun value
The fun value is a random number in Undertale, selected on Reset, between 1 and 100. This mechanic determines the occurrence of several rare events in the game; many of these events link to W.D. Gaster, the royal scientist before Alphys. These can range from Cell Phone calls, slight visual differences, or NPCs or locations appearing.
| Fun value | Event | Chance | Notes |
|---|---|---|---|
| 2–39 | Wrong number song | 38% | |
| 40–45 | Sans's call | 6% | |
| 46–50 | Alphys's call | 5% | |
| 56–57 | Nightmare mode | 2% | |
| 61 | Gaster follower 2 | 0.2% | 20% chance to appear if the fun value is right. |
| 62 | Gaster follower 1 | 0.5% | 50% chance to appear if the fun value is right. |
| 63 | Gaster follower 3 | 0.5% | 50% chance to appear if the fun value is right. |
| 65 | Sound Test room | 0.5% | 50% chance to appear if the fun value is right. |
| 66 | Fake hallway | 1% | |
room_mysteryman |
0.1% | 10% chance to appear if the fake hallway is found. | |
| 80–89 | Clam Girl | 10% | Does not appear during the Genocide Route. |
| 81 | Goner Clam Girl | 1% | Only on the Nintendo Switch and Xbox version. Does not appear during the Genocide Route. |
| 90–100 | Goner Kid | 11% |
Oh it's the wrong number! The wrong number song!
We're very very sorry that we got it wrong!
Oh it's the wrong number! The wrong number song!
We're very very sorry that we got it wrong!The wrong number song
The wrong number song plays in Snowdin Town, in the River Person room, if the fun value is within the range 2 to 39. The phone call begins asking for somebody whose name starts with the letter "G". The caller then recognizes that they dialed the wrong number, and proceeds to sing the wrong number song. This phone call is speculated to be for Gerson, Glyde, Gyftrot, Grillby, or W.D. Gaster. Even in the Japanese localization, the initial greeting is in English so as to give no further hints to what character it could be.
There is a known glitch with the wrong number song where the avatar of whomever the protagonist spoke to last shows up as the ID of the call. This glitch was patched in version 1.001.
If the fun value is between 40 and 45, Sans calls the protagonist in Snowdin, near Papyrus's cardboard sentry station. He asks if their refrigerator is running, and his response varies depending on what answer is chosen; if it is, he offers to "deposit the brewskis", and if not, to "send someone over to fix it".
If the fun value is between 46 and 50, Alphys calls the protagonist in Snowdin, near Papyrus's cardboard sentry station. She ostensibly orders a pizza and attempts to text the protagonist the toppings but instead ends up sending ASCII art of an anime cat girl (possibly Mew Mew). The protagonist's old phone cannot receive this, so it is read out character by character.
This occurs when the fun value is between 56 and 57. On the Monster Kidz Word Search in Snowdin, the puzzle additionally contains a bear-faced snowman called "Nightmare".
Three monsters may appear near Hotland elevators if the fun value is between 61 and 63 (one for each value). They talk about W.D. Gaster, the royal scientist before Alphys, and his fate.
The least likely one to appear speaks in rhymes, and disappears while snd_mysterygo plays after admitting to the protagonist it is holding a piece of Gaster. The other two stay around after they finish talking, but reset the fun value to 0 on appearance, so they do not reappear when re-entering their respective rooms.
By traveling upwards from the "Box Road" SAVE Point intersection in Snowdin, if the fun value is set to 65 and Papyrus has been defeated, there is an additional 50% chance for a hidden "Sound Test" room to appear. The menu itself contains three very short looping tracks and a longer track that, once picked, cannot be deselected. None of these tracks are used anywhere else in the game.
Happy Town (JP: ハッピータウン) is a short, cheery jingle with the filename mus_st_happytown.
Meat Factory (JP: ミートファクトリー) is a short robotic track with the filename mus_st_meatfactory.
Trouble Dingle (JP: トラブルディングル) is a short series of seemingly random robotic noises with the filename mus_st_troubledingle.
Upon selecting Gaster's Theme (JP: ガスターのテーマ), no other tracks can be selected. After it plays for 20 seconds, the room ceases playing music and displays a screen with the text "Thanks for your feedback! Be seeing you soon!" The protagonist is then returned to the room with the fishing pole. The track's filename is mus_st_him.
spr_mysteryman from the room accessed via the fake hallway.The fake hallway is a hallway in Waterfall that appears if the fun value is 66. It can appear between the "Crystal" SAVE Point and the Sans's telescope rooms. Once the protagonist enters this hallway the fun value is set to 0, including in the persistent undertale.ini file, so they cannot enter it again.[1]
There is an additional 10% chance for the mystery man to appear behind a gray door in this hallway. Once interacted with, they fade away to snd_mysterygo. The room is internally referred to as room_mysteryman.
Clam Girl appears at the "Quiet Area" SAVE Point if the fun value is between 80 and 89 and the protagonist is not on the Genocide Route. She talks about the protagonist meeting "Suzy". If the fun value is exactly 81 on the Nintendo Switch and Xbox version, she becomes a Goner NPC with additional dialogue.
A gray version of Monster Kid, internally referred to as spr_mkid_goner, can appear in room_water7 (room 91 in most versions and room 92 in the Xbox version) on a dock right before the room where Undyne first throws spears at the protagonist if the fun value is 90 or greater.
This character has additional dialogue if brought an umbrella, which can be found in the room after the statue that is being rained on. After exhausting the new dialogue with the umbrella and leaving the room, Goner Kid no longer appears.
The fun value can be modified using a text editor on line 36 of file0 and the "[General]" header of the undertale.ini file. These files are stored at the following locations by default:
- Windows:
- Windows XP: %SystemDrive%/Documents and Settings/%USERNAME%/Local/Application Data/UNDERTALE
- Windows Vista and later: %LOCALAPPDATA%/UNDERTALE
- Linux:
- DRM-free: ~/.config/UNDERTALE_linux
- Steam: ~/.config/UNDERTALE_linux_steamver
- Steam (later versions): ~/.config/UNDERTALE
- Mac: ~/Library/Application Support/com.tobyfox.undertale/
The presence of fun events is dictated primarily by line 36 of file0, internally referred to as global.flag[5]. Several of the events additionally require the named value in undertale.ini to match that of global.flag[5].
- Several fun events are triggered regardless of the fun value if debug mode is enabled through game modification.
- Before v1.001, the fun value was capitalized as "Fun value" in several code checks and thus made those events (Nightmare mode, Gaster Followers, the Sound Test room, the fake hallway, and Goner Kid) inaccessible without file editing.
- ↑ gml_Object_obj_door_ruins13_Alarm_2 script, lines 103–105