The Butt Witch is the main villain of the Cartoon Network series, Twelve Forever. She is voice by Matt Berry, who also does the voice of Allen from Aqua Teen Hunger Force.
12-year old Reggie Abbott visits an amazing world to live out their superhero fantasies as "Twelve" and escape the responsibilities of impending adulthood. One day, she threw a box of grown-up magazines into a green volcano, where she accidentally unleashed a monster who she nicknames "The Butt Witch".
When the Butt Witch found that her world was so childish and cute, she found it repulsive. She figured it was Twelve who was responsible for that, so the witch made it her purpose to destroy her. She tried to ridicule Reggie by forcing adulthood onto her, but she get thwarted every time.