The most likely reason you see a figure (if you ever did) in the mirror when you’ve played Bloody Mary: depriving your senses and straining your eyes in the dark like that will cause you to hallucinate after a decent amount of time. It’s why this game exists in some shape or form all around the world for centuries in different ways (young girls forever ago doing it as a way of predicting their future husband, if you’ve listened to TGC they talk about it in a song), if u stare in a mirror in the dark for a long time you’ll start to see shit and everyone was like oh shit!!!!!!!!!!!!!! Karen get in here try this!!!!
Why you still shouldnt do that shit: when u put a lot of intent into a ritualistic thing like that and it involves mirrors, known conductors of spirits, you’re not gonna invite Bloody Mary or Pig Face or whatever version of the game you know is called, but you could invite something. It’s the same reason you don’t say certain things during ouija board sessions that equate to inviting the spirit to respond or interact with the room around you, you’re telling them its okay to be in your home and once that happens it’s hard to get them out.