The most common story told is that Mary Worth was a witch that lived over 100 years ago who dabbled in the black arts. She was found out and executed.
The other story is more modern – a local woman was involved in a fatal car accident, and her face was horribly scarred before she died. She reappears in the mirror when summoned with that same horrific face.
Try play Bloody Mary if you dare, but don’t blame me if you find yourself trapped in a ghostly netherworld with the ghost of Bloody Mary forever!