Eons before the events of the series, Teeth was discovered abandoned and alone in a bucket of jawbreakers by Bill Cipher, along with the rest of his gang[2], who decided to adopt him as their pet.
Teeth with the rest of Bill's gang as Weirdmageddon begins.
In "Weirdmageddon Part 1," during the cold open, Bill introduces Teeth with the rest of his friends to the residents of Gravity Falls. Afterwards, on Main Street, Teeth and the other demons watch Bill turn Ford into a lifeless golden statue, taunt Dipper and burn the journals. He then tells Teeth and 8 Ball to eat Dipper as a reward. However, Dipper manages to get away from them. Later in the episode, after Time Baby and the Time Paradox Avoidance Enforcement Squadron are vaporized, Teeth and 8 Ball approach Bill to warn him that Dipper is still roaming free, and might try to free Mabel from her prison bubble. However, Bill is not worried, as he has the recently-prison escaped Gideon Gleeful on the case, so the party carries on.
In "Weirdmageddon 2: Escape From Reality," Teeth 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. Teeth is seen missing one of his teeth after the collision, though he is later seen without missing teeth. He and his comrades are then subjected to Bill's rage over the situation.
Teeth being sucked back into the Nightmare Realm as Weirdmageddon ends, but not before regurgitating Shmebulock unharmed.
In "Weirdmageddon 3: Take Back The Falls," Teeth participated in the battle against the Shacktron. Following the monsters' defeat, he flees, screaming while his back is currently on fire. After rounding up the townsfolk with his comrades, he eats Shmebulock in response to Grenda Grendinator's claim that they would rather die than surrender. Following Bill's defeat, Teeth is sucked back into the Nightmare Realm along with the rest of Bill's gang, but not before regurgitating Shmebulock unharmed.
Appearance
Teeth is a demon resembling a pair of dentures with large and white teeth and elongated pink gums that act as humanoid limbs, as well as a small pink aura.
"BLERRGGGH!!!" —Teeth regurgitating Shmebulock unharmed as he is sucked backed into the Nightmare Realm as Weirdmageddon ends.[source]
Trivia
Teeth without his aura. Notice how his hands come from his mouth rather than behind it.
During "Weirdmageddon 2: Escape From Reality," for some reason, he lacks his pink aura, also his hands come from inside his mouth rather than behind it.
In a deleted scene from "Weirdmageddon Part 1," it is revealed he was supposed to be a wind-up toy rather than an actual set of teeth, as a bolt can be seen his mouth; these bolts are hard to see due to his visibility on-screen and it is unknown if he was supposed to have a winding key powering him. (Gravity Falls: The Complete Series)
