Dark World
That is the Dark World, Susie.
An alternate view of reality through the lens of shadow.
In other words...
... an illusion.Ralsei's explanation of Dark Worlds, Chapter 3
A Dark World (JP: 闇の世界) is an alternate reality inhabited by Darkners. Dark Worlds are brought into existence by Dark Fountains and exist within various areas of Hometown/the "Light World". Dark Worlds are where the majority of Deltarune takes place.
Dark Worlds are powered by Dark Fountains, which a Lightner can create by projecting their "determination"[1] into a sharp object and piercing the ground.[2] When the surrounding environment becomes subsumed in darkness, the Fountain gives form to a Dark World.
Each Dark World consists of the contents and environments of the location where it was created, although a Dark World can appear much bigger than the location's real size. For example, the Hometown location of the Card Kingdom Dark World is the unused classroom, which contains a rug with a similar colors to Field, a checkerboard corresponding to the Great Board, and a cupboard filled with playing cards similar to Card Castle.
Dark Worlds are capable of giving digital files and images shown on wall posters physical forms, as shown in the Cyber World, where multiple Darkners that are the personifications of digital concepts (such as computer viruses, pop-up advertisements, and anti-virus software) can be encountered, and a poster of a Ferris wheel on the wall is shown to have turned into an actual Ferris wheel in Queen's Mansion.
Several Dark World objects have much more mundane Hometown equivalents: Kris's weapons correspond to pencils or an Eraser, and the Shadow Crystal corresponds to a shard of Glass. However, some objects, such as Noelle's Silver Watch, the Egg, and the BlackShard, directly match their Hometown counterparts.
Lightners can visit Dark Worlds by entering their corresponding Hometown locations. Lightners have only been able to leave Dark Worlds via three methods: by sealing that world's Dark Fountain, by using the Castle Town entrance, or exiting through a Great Door that leads to the Light World. Darkners can be transported between Dark Worlds by Lightners moving their Light World counterpart objects.
Dark Worlds can directly connect to each other if their Fountains are physically connected through an unlocked door, as shown with the closet Dark World and Card Kingdom, as well as the Dark Sanctuary and 3rd Sanctuary.
If Lightners receive harm in the Dark World, this is reflected in their HP in Hometown. Specific injuries also carry over to the Light World, as demonstrated by Berdly; if Berdly injured his arm following the battle against Queen, he returns to the Light World unable to move his arm.[3] Similarly, if Berdly is defeated by Noelle's fatal spell in the Chapter 2 Weird Route, he does not wake up with the other Lightners after the library Fountain is sealed, later appearing in the hospital in a comatose state.
Kris and Susie first enter the closet Dark World through a supply closet at their school. This Dark World contains the one and only pure Fountain of Darkness. After defeating King and sealing Card Castle's Eastern Fountain, Kris and Susie return to Hometown.
The following day, Kris and Susie revisit the closet Dark World. After meeting up with Ralsei, Kris brings some of the contents from the unused classroom to the closet, allowing the former inhabitants of Card Kingdom to live on in Castle Town. This practice gets repeated later with other recruits. However, Card Kingdom can no longer be visited, as its Fountain had already been sealed.
Later on, Kris and Susie (along with Berdly and Noelle) go study at the library, only to find that the computer lab, too, harbors a Dark Fountain. This Dark World, the Cyber World, is ruled over by Queen. After defeating her and sealing the library Fountain at her mansion, Kris and Susie return to Hometown once more.
In the middle of the night, Kris creates a Dark Fountain in the Dreemurr residence's living room, turning it into a Dark World, which later acts as the main location of Chapter 3.
Kris's Dark Fountain transforms the living room into TV World, where they and Susie wake up at the start of the Chapter. After defeating Tenna and being bested by the Knight, they exit TV World.
At the end of the Chapter, it is revealed that a Dark World exists inside the shelter.
Kris and Susie are shown sealing the Dreemurr residence Fountain at the start of Chapter 4. After visiting Noelle's House and optionally returning to Castle Town, Kris and Susie go to check up on Toriel at the church. There they discover a newly-created Dark World, which they enter. After traversing the Dark Sanctuary, the team finds and seals the Dark Sanctuary Fountain, before discovering another one in the church's hall, blocked off by a locked door.
In an attempt to get the code for the lock, Susie creates a Fountain in the church's lobby, which creates the 2nd Sanctuary. Upon exploring and sealing this Dark World, Susie and Kris are able to unlock the door and enter the 3rd Sanctuary in the hall. While traversing through this Dark World, the team encounters the Knight again, who creates a Fountain within the Dark World. This causes the emergence of a Titan, who serves as the final obstacle before Kris is able to seal the 3rd Sanctuary's Fountain.
These are the currently known locations within the Dark World, ordered by when Kris and their party visits them.
- Closet Dark World (School: supply closet)
- Card Kingdom (School: unused classroom)
- Cyber World (Library: computer lab)
- TV World (Dreemurr residence: living room)
- Dark Sanctuaries (Church)
- Attempting to use the Cell Phone in any of the Dark Worlds prompts an unskippable audio cue. Said audio cue is a snippet of
mus_smile, which also plays in one of Undertale's inaccessible rooms,room_gaster.
- ↑
That Is When I Realized
— Queen, Chapter 2
This Power... This Power Of The Will
This Power Of Determination...
Is This Not Something That All Lightners Possess...?
If One Was Simply
Determined Enough
Could Not Anyone Make A Dark Fountain? - ↑
Noelle
— Queen, Chapter 2
Darling
Honey
Sweetie
Gravy
Take... The Pin... I Gave You
And... Stab The Earth
Creating... Our New... Supreme Empire - ↑
Just a little CHECKUP, Susan. I slept on my arm.
— Berdly, Chapter 4
... And now, it won't... wake, up.