Dream Castle is a giant castle realm where imagination lingers onto itself, creating a strange mazelike world. Creatures such as the Dubstep Chest, Head Centipide, and Porkwingster reside. It is featured in both The Adventures of Ismail and Doodleland RPG: Mazing Adventure.
The Dream Castle only appears if someone is trapped into a dream by another person. It is a magical realm and can be controlled from the outside but not in the inside.
The only way to escape is breaking the beacon block. Dieing will just land you into lower levels of the Dream Castle.
Additionally, on higher levels, dream fabrication becomes much stronger, while on lower levels it is nearly impossible.
The Dream Castle can also turn rooms into clones of other realms. It can also turn a person's memories into fabrication without them knowing, allowing the past and possible future to coexist.
This becomes very apparent in Doodleland RPG: Mazing Adventure, where players can fight all incarnations of Dark Scribble, including his true form which is still in darkness. Jazz and Framework also appear, despite being dead.