Keyhole is a minor antagonist of the Disney XD series Gravity Falls. He is a demon and a interdimensional criminal from an unknown dimension and one of Bill Cipher's friends.
Keyhole has a blue humanoid body with a forehead that resembles a keyhole. Keyhole has a darker shade of blue around it's eyes, a pink nose and a small blue aura.
Not much is known about Keyhole's past, except for a few details. Eons before the events of the series, Keyhole commited crimes before being called together by Bill Cipher, along with 8 Ball, Amorphous Shape, Hectorgon, Kryptos, Xanthar, Paci-Fire, Pyronica, and Teeth. Ever since, he had helped Bill to open a gateway to the real world so the Henchmaniacs can enter it and make a neverending party.
In "Weirdmageddon Part 1", Bill introduces Keyhole along with the rest of his demon friends to the residents of Gravity Falls. Afterwards, on Main Street, Keyhole and the other demons 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 invaded the Fearamid, but to the demon's delight Bill vaporizes Time Baby and his squadron except Blendin. The party then continues as Keyhole and the other demons 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 which makes Bill considers getting Ford 'out of retirement'.
In "Weirdmageddon 3: Take Back The Falls", Keyhole along with Bill's minions attacked the Shacktron during the giant monster fight. But was defeated by the Shacktron. He was sucked back to the nightmare realm following Bill's defeat along with the rest of the nightmares.
It's unknown what happened to Keyhole along with the other Henchmaniacs afterwards.