Relation to SlendermanEdit
While in the book they resemble humans with tentacles protruding from their mouths, in the film adaptation their design was clearly far more based on Slender Man, as they are portrayed as bald, pale, unrealistically tall, wearing suits, and are missing most of their face.
Even without the visual similarities, both possess tentacles, are very tall in stature, and prey on children. In the books, they fed on the children's souls, while in the films they consume their eyes. Also like Slenderman, most people are unable to see them.
The main difference is that the Hollowgasts origin are known, and they can be controlled by others, rather than being the ones in control like Slender Man.