Catoptromancy
Catoptromancy (Greek katoptron, mirror) is divination by gazing into a mirror, especially in shadowy environments. Practiced in ancient Greece (oracle of Demeter in Patras) and Rome. The "Bloody Mary" of modern Anglo-Saxon urban legend is a folkloric descendant.
Method
Gaze fixedly into the surface of the mirror, in dim light. Visions, words or impressions may appear. Variation: hydromancy using a water surface as a mirror.