Bloody Mary was Mary Tudor, Queen of England, and daughter of King Henry the 8th and Catherine of Aragon. All her life, she was a mean brat to her little sister, Elizabeth and her brother Edward VI. She did not like them at all and was very jealous. When Edward VI died, she became Queen Mary of England. She was hated all over for changing the religion in England from Protestant to Roman Catholic. She mass-murdered over 100 Protestant leaders, earning her name as "Bloody Mary".
And yes, I have seen Bloody Mary. My friends and I decided to try it out. This is what we did:
1) We went into the bathroom.
2) Turned out the lights.
3) Ran the water.
4) Spun around 3 times saying "Bloody Mary."
5) Closed our eyes and held hands until we heard anything. (not saying this way is right or wrong, we just did it like that.)
There was a low 'thump' and we opened our eyes. There was a bloody dark-haired girl covered in blood. But it was very very dark, so very hard to tell. All she did was look at us, like an image painted on the mirror. Then we got scared and turned on the light, and whatever it was, was gone.

This is the true story of Bloody Mary.