The Grand High Witch
The Grand High Witch or Miss Ernst was the leader of all the witches in the world in the film and book, The Witches. She attempted to turn children that attended her fake convention into mice, in order for them to be eaten.
Jessica Lange played the Supreme witch in American Horror Story: Coven. Fiona was wickedly evil. Her powers ranged from pyrokinesis, telekinesis, divination, and clairvoyance. She would kill anyone that would dare cause harm to her and the coven.