Legalities of using slenderman in a story?

It's not a slenderman story, but I was thinking of having slenderman in it. The story revolves around a town with an abnormally large amount of urban legends as well as ghost and monster sightings. It deals with spirits which are manifestations of the human mind. They are highly belief driven, the spirit world itself is connected to the dream world. While they usually cannot be seen by normal humans, when they are they often take the form of how they are expected to be seen. A cat spirit might be seen as a normal cat. Or a benign and non-hostile ghost might be seen as something out of a horror movie. It all depends on who is the one seeing it. To emphasize this, I wanted to throw in some creatures from modern urban legends.