If you turn off the lights and say "bloody Mary" three times nothing will happen...at first... Once you go to sleep you will start to have nightmares about bloody Mary for about two weeks. Eventually you will start to hear noises and stuff around your house an this could go on forever but eventually she will murder you. That is why some people think that they hear ghosts. It is really bloody Mary but they don't remember saying bloody Mary when they were young. Whatever you do DO NOT SAY BLOODY MARY 3 times in a mirror. She will kill you eventually but it may take 10,20, or even 50 years
The other people talking about alcohol are not actually reading the question. Is bloody Mary real? Yes, she is. The game where you spin in the mirror with the lights off is not real, but I do believe in the super-natural.