THIS NOT FINISHED!!! He is tall and faceless and has tentacles and he has teleportation and if you look in his faceless face he will stalk you then either kill you or take you to a place where you can not escape and he will stalk you forever.

He has 2 video games: slender the 8 pages and slender the arrival 

references: in plants vs zombies: garden warfare go to the zomboss estate look behind the trees and you will see him he doesn't do anything and you can't kill him.