- Main Article: Nightmare Bitters
Nightmare Bitters is the Nightmare version of Miss Bitters, and seemed to be the ultimate authority in the Nightmare Realm.
- Main Article: Nightmare Dib
The Nightmare version of Dib. He was locked in the Nightmare Version of the Crazy House for Boys, and has a lobotomy scar on a head that's even bigger than that of his "real-world" counterpart. For most of his time onscreen, he remained in the darkness, only revealing his face once.
- Main Article: Nightmare Membrane
- Main Article: Nightmare Gaz
Nightmare Gaz is the Nightmare version of Gaz, and was seen in Dib's Nightmare House, whilst drinking "Dark Poop" soda.
Nightmare White Coats
- Main Article: Nightmare White Coats
- Nightmare White Coats were the Nightmare Versions of the White Coats, who work worked in the Crazy House for Boys.
Main Article: Nightmare NnyNightmare Nny is a Nightmare version of the real Johnny C and due to his appearance in the Nightmare realm, it can be implied that Dib and Nny met off-screen.
Hummelflesh, Destroyer of Worlds
- Main Article: Hummelflesh, Destroyer of Worlds
He seemed to be the leader of the Halloweenies (after Nightmare Bitters) until he failed in bringing Dib to Nightmare Bitters.
- Main Article: Yolk
He was the Halloweenie who was sent by Nightmare Bitters to capture Dib after Hummelflesh failed.
- Main Articles: The Enigma
He was the Halloweenie who attempted to reassure Nightmare Bitters when she felt stupid after saying "Let the head... thingy... start!"
Other Halloweenies are:
- The Admiral
- Bobby Joe Ray Billy Sue
- Bride of Mortïs
- Cage Monster
- Dancing Skeletons
- Gordon Peterson and Gordon Peterson Jr
- Mr. Pinchy
- Puncher of Heads
- Simon Rikkis
- Interestingly, despite the fact that all the Hallooweenies are in Dib's mind, none of them seemed to recognize that Zim is an alien.