Bloody Mary is a game kids play in a bathroom. Someone will go into a bathroom, either turn off all of the lights, and light a candle, or just stay in pitch black. Then, they will look into the mirror and chant "Bloody Mary" over and over again. The idea is that after chanting her name, "Bloody Mary" will appear to them in the mirror. And she is supposed to be any number of things: a victim of some horrific accident or crime, a witch burned at the stake hundreds of years ago. Whatever you are supposed to see, most kids get so freaked out and bolt from the bathroom before they see anything.