The Demon in Disguise Slenderman x Reader

Warning: Contains (or will contain) the following: Gory descriptions, violence, mature themes, etc.
My name is Mary. I may not look it, but I have a problem. A BIG problem. Like one that could get me sent to an asylum kind of problem. But, I decided to hide it. When the secret got out... I... I ran from home. Then a certain someone found me.