This is a story that happened to me when i was much younger.
I was maybe, 14 or early 15 and this occured to me.
I was just browsing a random website about sadness, when something opened up, it was a page named [--4ifgir--CONFIDENTIAL---4ifgir--] and one of the pictures shown to me was about a guy, croutched down staring into a wall, surrounding him with darkness. After i scrolled down a little bit, it shows another picture showing a man with a top hat, a tie, suit and weird, pointy hair killing a middle aged man and a young woman with one slash from a knife, with a description saying 'sinners will be punished' thats when i accidentally clicked it to zoom in, where the image starts blinking from the man in the top hat, smirking. I quickly closed the website and went to bed.
Later, at night, i dreamed that through a camera i saw a man smiling, all i saw was his mouth, then it switched to an empty corner of two corridors. I was issued to be a security guard, as i finnally noticed after seeing those two cameras. After i checked other cameras, i saw him, the same guy from the website, still wearing the top hat. He was just smiling towards the camera, showing his knife and showing a note saying 'im coming for you'. I quickly locked my door and only seconds after that, i saw something move in the camera, it was very fast, like a shadow passing through. Then, i heard a knock on the door. I didnt dare to open it, but then, i felt something sharp in my stomach. It was his knife pearcing my stomach. I then bled out.
I woke up from that terrible nightmare. Noticing it was all a dream, i tried looking around and i froze when seeing that same man, just sitting outside my door. I got extremely terrified, as i fell down my bed. I tried going towards him to see if it was nothing but a visage, but then, it felt like, every step i did was...like he tried to kill me, telepathically. Every step i took, i felt weaker and weaker, until i reached the door, where i fell slumped trying to walk away from it, to warn my parents, but i didnt have the strength to get up and move, not even a finger is barely movable. I was still alive, but i could not move, i was completely paralyzed. As the man stood up and tried to open the door, i layed down, closing my eyes, crying and i died.
As i woke up completely from that nightmare inside a nightmare, i felt deeply traumatized. I knew he was still among me, but i was not sure if he meant me any harm. I became very afraid and im not sure if it will ever happen again, or if he even exists. This is a true experience from what happened to me one night, it still chills my spine talking about it. I dont get scared too easily, but that 'thing'...he scares me..but if he ever appears to you, then remember that he might be there to either kill you, or try to keep you safe. Im not sure if he tried to kill me, but it felt like it with his telepathic abilities and his knife. But either way, stay safe and hope for the best. There is no proper name for him, but i think we could just call him 'the man with the top hat' because that was who he was.