No one knows who Bloody Mary really was. By most accounts she was a woman named Mary Worth who was involved in an automobile crash and was disfigured. Another thought is that she was a witch that was burned at the stake.
Bloody Mary is a known legend since over a 100 years ago that has many different stories of who she was. It is a myth based on a true story but Has become twisted and retold different ways so it is hard to say what the real story is or was.
She is real. Very real. But for some reason she only hurts girls. She is jealous. but it is safe to play as long as you DON'T TOUCH anything that she gives to you or goes near you while you play. Only if you do can she hurt/kill you.