The Slender Man is a supernatural creature that is described as appearing as a normal human being but he is described as being 8 feet tall and he has vectors or extra appendages that are described to be as sharp as swords. The creature is known to stalk humans and cause many differences. He is described as a shadow creature that has missing a face. The creature fits into many mythologies in legends from nations such as germany and celts which brings up the possibility that he could be real. A man named victor Surge found this legend and made his own version of it which he called slender man. The slender man is not exactly evil according to mythology but victor Surge's version shows him as an evil creature that stalks humans to kill. In mythology he was actually trying to save you from a painful death by taking you to the under world early.

Personally I believe he is real but not victor Surge's version. The problem is figuring out what came from mythology and what was made up for entertainment. For example, People say that Hans Holbeins wood cut Der Ritter or the knight was referring to the slender man but with closer examination you will see that the four arms on it were photo shopped to the original version of the dance of death series. The video that was shown two your cousin was probably from the youtube channel Marble Hornets or Totheark. Those two channels are the closest thing we have to a movie about him even though it is pretty convincing they admit it is fake and was done for entertainment.

The slender man has become an internet Meme and there have been many sightings of him watching people outside of their house. I am not really sure what to tell your cousin but slender man is basically a monster that appears out of the shadows to kill people. The photo shopped images of the slender man kind of turn it into a game like can you see him because he is hidden in the background of every picture.

He is also described to be wearing the clothes of people he killed like a bushiness suit or something and somebody also said that he can walk on his limbs like doctor octopus from spider man. His face is described to be hidden over a piece of flesh pulled over it but it is obvious that it is a skull because he lacks the muscles in it. He seems to want to blend in with humans like he has an inefficient knowledge of humans.