The ending...

I think at the end, we are to assume that he has seen the video before, this is just the first time that he is showing the audience the footage. When he is introducing the video that has been left, his eyes look all red as if he hasn't slept. We are meant to come to our own conclusion of what happened after they were woken up.

I assume Adam was shaken up by the fact the monster woke him up and threatened not only himself but his wife, plus the footage that Dekker is now caged up like some animal. I would say that the reality of that thing being in your home and you literally feeling it's anger in the flesh, has more of an impact than it literally sneaking in and leaving the camera at your bedside and the shock that would ensue. Your home after-all, is supposed to be one's safe little sanctuary.

Could it be that the monster at the end was Dekker? I don't know why, but that's the first thing that crossed my mind while watching. Maybe the monsters turned him into one of their own and then sent him to Adam's house. Or maybe he escaped, or whatever...

Yeah, it seemed like they put that there just for the sake of the jump scare but it really makes the ending less effective. If he were just showing us a creepy video of Dekker and of someone coming into his home and filming him, it would all track. And that is obviously what they're telegraphing the whole time, the classic unsettling "I was inside your house!" scene. Then they throw in the jump scare to shake our expectation. But it just muddles the sequence of events.

The shout at the end seems to imply a bad end for the couple, but he's showing us the video that someone is supposed to have sent to him. Obviously this video isn't a surprise if he wakes up at the end of it and has an encounter with the deliverer that we don't get to witness (naturally, why would we care to see the most interesting and pivotal scene in the film?). So why does he show us the video as if it were self-explanatory? It clearly isn't. It leaves a bunch of questions unanswered. It doesn't really add up with the rest of the story. If he were truly afraid for his life or his wife's, he wouldn't show that video at all. But if he were interested in the truth, why not show us the whole thing? Or at least tell us what happened?

Why does the clip cut out at that exact moment? That was very obviously a choice made by Adam Green the director, not Adam Green the character within the mockumentary. It's a cheap scare that just disturbs the suspension of disbelief.