In spirituality, a mirror symbolizes spiritual reflection. The spiritual mirror reflects consequences of actions that are both negative and positive.
Since mankind first saw its own reflection, we have been fascinated by surfaces that cast our image back to us. Possibly because of that fascination, there is an incredibly wide variety of superstitions, myths and urban legends surrounding mirrors specifically and reflective bodies in general.
Everyone has heard, for example, that breaking a mirror will bring seven years of bad luck. This superstition dates back to the Romans, who believed that life renewed itself every seven years, and that breaking a mirror would thus cause damage to the soul it was reflecting at the time for that duration.
Urban legends have long held that spirits could be contacted through mirrors. Stories abound about what has happened to people who go into a dark room, look into a mirror and call a known and dangerous spirit several times. The most famous of these stories is Bloody Mary-- and while many dismiss the claims, others will tell you in earnest about experiences in which they saw something, found unexplained scratches on their bodies or experienced paranormal phenomenon for weeks after the stunt.
Bloody Mary is a folklore legend consisting of a ghost, phantom or spirit conjured to reveal the future. She is said to appear in a mirror when her name is called three times. The Bloody Mary apparition may be benign or malevolent, depending on historic variations of the legend. The Bloody Mary appearances are mostly "witnessed" in group participation play.
Mary Tudor was the sister of Queen Elizabeth I of England, the two daughters of Henry VIII. It was a turbulent time in Britain, with Catholics and Protestants violently opposed to each other. Mary was a Catholic, and had so many Protestants put to death through vicious means such as burning at the stake that she earned the nickname 'Bloody Mary.'
Horror movies tend to shy away from the 'Mary Tudor was Bloody Mary' explanation, relying as it would on period costume and a British setting, and thus the Urban Legend has changed over time and taken on a life of its own....