Marnie Piper is the main heroine of the Disney's live-action series Halloweentown. She is the elder sibling of Dylan and Sophie, the eldest daughter of Gwen, and the granddaughter of Aggie Cromwell. A half-human witch (inherited from her grandmother), Marnie was destined to stop the rise of a demon in Halloweentown, a realm inhabited by demons and witches; thus she was tutored by her grandmother in the teachings of witch-craft to counter the threat. She eventually managed to master her craft, battled the demon, who was no other than the Mayor of Halloweentown (otherwise known as the sorcerer Kalabar), and saved the realm from his threat.
Regarding the villain wars, Marnie appears as one of prominent heroes of the live-action universe during the events of the second Disney Heroes vs. Villains who battle the forces of evil. While she initially appears as an amateur witch, she gradually becomes into a powerful spellcaster.