When I was little, maybe middle-school age at oldest (can't remember the exact year) my family lived with my heavy Christian grandparents. The room I slept in at the time of this story even had a Bible sitting next to the CRT TV.
I never really woke up in the middle of the night unless I had nightmares. This one night I woke up in the middle of the night, no dreams had at all, and I saw a shadow man standing in the open doorway. I closed the door every night. And the shadow man - it wasn't like an actual 3 dimensional person, he was like a 2D Shadow that stood like a man, no face, literally just like a shadow. It didn't move, it just stood there.
This wasn't sleep paralysis - I could move and make noise, and I felt an overwhelming amount of fear and anxiety. I silently cried, trying to play dead. I eventually fell back asleep, and the next morning I asked everyone in the house if it was them checking on me. Not a single one of them had checked on me that night. The door was also still open in the morning.
The weirdest part? The shape of this shadow man looked exactly how my older brother looks now, over 10 years later, and back when this happened my room was directly next to my brother's. It wasn't a dream. It wasn't sleep paralysis. I know what I saw that night, and I will never forget the experience I had. This is why I believe in ghosts and demons.
Whether people believe me or not is up to them, but I will always swear this was all real. I've had real feeling dreams. This was not that. The door couldn't open itself.