Paci-Fire

 is a demon and an interdimensional criminal, from an unknown dimension, that appears during the events of Weirdmageddon.

Background
Eons before the events of the series Keyhole indulged in criminal activities before being call together along with 8 Ball, Amorphous Shape, Eye-Bats, Hectorgon, Kryptos, Teeth, Pyronica, and Xanthar by Bill.

Season 2
In "The Last Mabelcorn," the arrival of Pacifier along with his demon comrade into Gravity Falls' dimension is foreshadowed during the episode's cold open after Ford receives Bill's warning that Weirdmageddon is coming Pacifier is briefly seen on an image of a wheel with symbols. However, the cross on its forehead isn't there but on the wheel its self.

In Weirdmageddon Part 1," during the cool open, Bill introduces Keyhole 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 of his journals. Later in the episode, Keyhole is seen drinking Time punch with Keyhole and enjoying the "V.I.P." party Bill is having at the Fearamid until Time Baby and the Time Police crash the party, but to the demons delight Bill vaporizes Time Baby and his squadron. The party then continues as Keyhole and the other demons rejoice over Time Baby's presumed death.

Appearance
Pacifier has the appearance of a demonic dark-grey baby with thick black horns, a pink bull-nose, red eyes, and a titular red pacifier being sucked by a second face on its torso. Pacifier also has a gold cross on its massive forehead with an eye similar to Bill's at its center and a red aura around its body. Neither of Pacifier's faces seem to change expression.

Trivia

 * In the early character design for Pacifier, instead having the gold cross on its forehead there was Bill Cipher's wheel. Additionally, Pacifier would have a tattoo on its left shoulder and a large almost flaming aura around its body.