I have a theory

I haven't finished the book yet but I have a theory. There is an entity with the ability to trespass through observation. Once observed directly or through media, this entity festers in the brain of the Observer causing insanity.

The entity can control the medium in which it was observed, eliminating it entirely, therefore shifting the framework of reality.

First observed in the labyrinth (where it was meant to stay) it travels through the Navidson exploration party to Zampano then while driving him insane it pushes him to write creating another piece of media for it to flow through. Once captured in Z's piece it erases all other traces of its own existence, all that's left of those things are in the ramblings of a mad man...

Ramblings which Johnny finds...