I don't know if the information I've garnered about the Slender Man will be helpful, but I will relay it to his victims just the same.
Surprisingly, Slender Man is highly human when naked. The only difference is his massive size. His torso is the size of a man of around six feet, but his arms and legs are far out of normal human proportions. His skin is lily white and completely hairless. He is a pleasure to touch, like running your hands over soft, warm silk. Though very little of him suggests that he is mamalian, he does have nipples, two of them--one on each side of his chest. He also has a navel, which tells me that he was born. Out of his back, he has ten small nubs. Five on each side of his spine, running down his back. They start just below his shoulders and go to his midback.. He has a buttocks and human genitalia. He is much more well endowed than any human man and he is uncircumsized. His nerve endings seem to be far more sensitive than a human's.
His body is much more thin, to a sickly degree. All of his bones are visible.
He does have a face, he can conceal it when he needs to, and only shows it to some. I have seen this face. His eyes are black and almond shaped, while his pupils are white. His mouth is lipless and filled with a row of canine teeth. His tongue is long, thin, and black. He has very high dexterity with his tongue.
He does posses a bodily odour, but it smells vaguely of fresh summer peaches. His blood is a deep violet colour, and his semen is periwinkle blue. He does need to "relieve" himself, like a human, and he does bathe. He enjoys cool water over hot. Hot hurts him.
All for now. More later.I am being watched by his Agents.