The Weird Sisters have played a major role in the history of Demona and Macbeth, and have also influenced the gargoyle clan living in Avalon. The Weird Sisters were set to task as the guardians of Avalon when Oberon cast out his children. They were to keep out all magic save Avalon’s own, and to prevent any of the children from coming home early. When the magus led Princess Katherine, along with the Gargoyle eggs, to Avalon’s safe harbor, the three tried to prevent them access. Tom cried that the eggs and the princess would die without Avalon’s safety. The sister’s declared that the party was "screeching like barn owls, about meaningless lives" and attempted to transform them into owls. The Magus managed to turn their spell back on themselves, turning them into barn owls and banishing them from Avalon. Shortly afterward the spell was broken by the Arch-Magus, who gave them a chance to get revenge against the Magus, in a few hundred years. He charged them with seeing that Macbeth and Demona would be available and ready for use when the battle finally arrived and to gather the magic items, the Eye of Odin, the Grimorum Arcanorum, and the Phoenix Gate. The three agreed, and set out to gain control over Macbeth and Demona. They accomplished this by linking the two, so that they feel each other’s pain and one could not die unless the other did, rendering them effectively immortal. They manipulated the two to gather the magical items, and later used them as shock troops against the Avalon Clan. The Magus gave his life defending the Princess and the eggs (now grown Gargoyles) from the sisters, diverting them from the chamber of the sleeping king, so that they would not know that the king had been awoken. But in his sacrifice he defeated the three again, keeping them from the people he loved and once again banishing them from Avalon.

They reared their ugly heads again, causing trouble for the Avalon clan, seemingly out of spite, though their main adversary, the Magus was gone. They were the ones that told Oberon of the Princess and her Clan. And they who recommended their destruction. That disaster was averted by the intervention of Goliath, Angela and Elisa Maza. They seem now to be acting as the lackey’s of Oberon, fetching wayward children of Avalon who refuse to come home for the Gathering.