My Hollowface is not your Hollowface (SPOILERS)

A few people have asked how the hallucination of Hollowface was transferred so vividly from Juan/John to his daughter. The explanantion I've come up with after watching the film a couple of times is this:

We know that Mia came up with the whole idea of Hollowface after finding the story her father wrote as a boy and copying it for school. It gave her nightmares, but she didn't see a hooded spectre at first - she saw herself with no face. When she told her father about the nightmares, he tried to dispel it by playing a game where they gave the monster a shape (building it out of a raincoat and a pair of boots) and burned it in the back yard. Of course, John was (perhaps inadvertently) recreating the monster he'd been afraid of as a boy. And it had the opposite effect to what he intended, by putting a clear image of that monster into his daughter's mind (which is why she looked so frightened as she watched it burn, and it seemed to be almost coming to life). From that point on, when Mia imagined her monster, it looked like her father's old monster - because he'd shown it to her.

But not exactly like his monster - go back to the opening scenes and you'll see that the creature attacking Juan and his mother is a sort of phony-looking CGI puppet, almost a poor man's ringwraith (a heavily-distorted version of his father). When it appears in Mia's bedroom later, it's much more solid and real-looking, and bears a remarkable resemblence to that raincoat they burned outside. When Mia falls into the fantasy at the end, Hollowface is even smouldering and has embers falling from him, because that moment on the lawn was when he became "real" to her.

(Or maybe it's a ghost.)