Nightmare King

The Nightmare King is the main antagonist of Little Nemo: Adventures in Slumberland.

He is released after Nemo unlocked the door that Morpheus warned him not to open. Nemo rushes back to Morpheus' castle in time for his coronation ceremony, where Nemo is handed the royal scepter, the only thing capable of defending Slumberland in the event of the Nightmare King's return. In the middle of a dance session between Morpheus and Genius, the Nightmare King reaches the castle and steals Morpheus away. As the partygoers search for a scapegoat, Flip reveals Nemo to be responsible for the Nightmare King's escape.

Nemo awakens in his home, which floods with seawater and ejects him into the ocean. Genius discovers Nemo and tells him not to blame himself for all that has happened. When the two return to Slumberland, Flip reveals that he has a map to Nightmare Land, where Morpheus is currently being held. Nemo, Camille and Flip set off in a tugboat in search of Morpheus. They are soon sucked into a whirlpool and find themselves in the monster-infested Nightmare Land. The trio comes across a group of shapeshifting goblins who wish to aid in the quest to find Morpheus. The Nightmare King sends a flock of giant bats to seize the rescue party. Nemo attempts to use the scepter, but awakens in his bed instead. The goblins appear in Nemo's room and the group travels to Nightmare Castle by flying through a hole in the sky. However, they are subsequently imprisoned in the castle, where the Nightmare King demands possession of the scepter. Nemo soon uses the scepter to finally eliminate the Nightmare King. Slumberland celebrates the fall of the Nightmare Kingdom, after which Nemo once more awakens in his room.