Bloody mary is a story that has been told for many of years now. Saying her name 3 times In A dimly lit room will make her appear. People have seen her ghostly figure in blood. Also many people have experienced demon like APPARITIONS after "summoning" her. The point was to see what their future would look like. She could be a mean or nice spirit. Her apparition could be screaming at you or cursing at you and steal your soul.
The old ritual was that women would walk up stairs backwards and look into a mirror, to see what their future husband would like. But there was a chance where a skull would appear, meaning that they would pass away before having a chance to marry.