I did that thing in like 5th grade at summer camp. We hiked all the way to the end of camp for some wilderness seclusion thing. We had to stay in the old dorm for 3 nights. Me and friends did the bloody mary thing and nothing happened. Then we went outside for a midnight walk in the woods (dont blame me, my friends are dumbasses). I ditched them and went back and had a good nights sleep. They apparently got lost and were locked out of the dorm for the night (I took the keys that they had taken with me back to the dorm). They knocked at like 3 am and got in a shitload of trouble.
ANYWAY, I tried Bloody Mary, and nothing happened.