Paci-Fire resembles a creepy dark-grey baby with enormous black horns, a pink bull-like nose, glowing red eyes, a somewhat scrunched face, small dark grey lips and a black tail. It also has a second face on its torso with light red eyes and red pupils sucking a titular red pacifier on a chain. Paci-Fire also has a gold cross on its massive forehead with a diamond-shaped eye similar to Bill's at its center and a red aura around its body.
Eons before the events of the series, Paci-Fire indulged in criminal activities such as murder on countless moons before being called together by Bill Cipher, along with 8 Ball, Amorphous Shape, Hectorgon, Keyhole, Kryptos, Teeth, Pyronica, Lava Lamp Shaped Creature, and Xanthar.
In "The Last Mabelcorn", after Ford receives Bill's warning that Weirdmageddon is coming, Paci-Fire is briefly seen on an image of a wheel with symbols.
In "Weirdmageddon Part 1", during the cold open, Bill introduces Paci-Fire with the rest of his friends to the residents of Gravity Falls. Afterwards, on Main Street, Paci-Fire and the other demons watch Bill turn Ford into a golden statue and taunt Dipper before burning the journals. Later in the episode, Paci-Fire 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. To the demons' delight, Bill vaporizes Time Baby and his squadron. The party then continues as Paci-Fire and the others rejoice over Time Baby's presumed death.
In "Weirdmageddon 2: Escape From Reality", Paci-Fire and the rest of Bill's friends attempt to leave Gravity Falls to spread their chaos across the world, only to collide with an invisible barrier. Paci-Fire complains that it might have broken something, but Bill angrily tells it to "walk it off."
In "Weirdmageddon 3: Take Back The Falls", Paci-Fire participates in the battle against the Shacktron. Following Bill's defeat, it was sucked back to the Nightmare Realm along with its comrades.