Keyhole is a character and an antagonist from Gravity Falls. He is a demon and a interdimensional criminal from an unknown dimension and one of Bill Cipher's friends.
Keyhole has a aqua humanoid body and a large forehead with a few orange spots on the side and a large hole resembles a keyhole. Keyhole has a darker shade of blue around its eyes, a small pink nose and small blue aura.
Eons before the events of the series, Keyhole indulged in criminal activities before being called together by Bill Cipher, along with 8 Ball, Amorphous Shape, Hectorgon, Kryptos, Teeth, Paci-Fire, Pyronica, Lava Lamp Shaped Creature, and Xanthar.
In "Weirdmageddon Part 1", during the cold open, Bill introduces Keyhole with the rest of his friends to the residents of Gravity Falls. Afterwards, on Main Street, Keyhole and the others watch Bill turn Ford into a golden statue and taunt Dipper before burning the journals. Later in the episode, Keyhole is seen drinking Time Punch with Paci-Fire and enjoying the "V.I.P." party Bill is having at the Fearamid until Time Baby and the Time Police crash the party. To the beings' delight, Bill vaporizes Time Baby and his squadron. The party then continues as Keyhole and the others rejoice over Time Baby's presumed death.
In "Weirdmageddon 2: Escape From Reality", Keyhole and the rest of Bill's minions attempt to leave Gravity Falls and spread their chaos across the world, but are stopped by an invisible barrier around the town. A short time afterwards, Keyhole informs Bill that Gideon allowed Dipper, Wendy and Soos to enter Mabel's bubble. Bill is unconcerned, believing that no-one can escape the bubble's temptations, and tells Keyhole to bring him Gideon and take the rest of the day off.
In "Weirdmageddon 3: Take Back The Falls", Keyhole participated in the battle against the Shacktron. Following Bill's defeat, it was sucked back to the Nightmare Realm along with its fellow nightmares.