Eons before the events of the series Teeth indulged in criminal activities before being called together by Bill Cipher, along with 8 Ball, Amorphous Shape, Hectorgon, Keyhole, Kryptos, Paci-Fire, Pyronica, and Xanthar.
In "The Last Mabelcorn," the arrival of Teeth along with his demon comrades into Gravity Falls' dimension is foreshadowed during the episode's cold open after Ford receives Bill's warning that Weirdmageddon is coming, Teeth is briefly seen on an image of a wheel with symbols.
In Weirdmageddon Part 1," during the cold open, Bill introduces Teeth with the rest of his demon friends to the residents of Gravity Falls. Afterwards, on Main Street, Teeth and the other demons watch Bill turn Ford into a golden statue and taunt Dipper before burning of the journals, after Bill burned the journals, he offers Teeth and 8 Ball to eat Dipper as a reward. However, Dipper managed to get away from them. Later in the episode, after Time Baby and the Time Police 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 bubble. However, Bill isn't too worried, as he has Gideon 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.
In "Weirdmageddon 3: Take Back The Falls," he participated in the battle against the Shacktron. Following the monsters' defeat, he was seen fleeing and screaming while he was on fire. After rounding up the townsfolk with his fellow nightmares, he ate Schmebulock in response to their claim that they would rather die than surrender. Following Bill's defeat, Teeth was sucked back to the nightmare realm along with the rest of the nightmares, vomiting out Schmebulock in the process.