"Why don't they put down the goddamned camera?"
It's the perennial question of found-footage videos; you'd think that, after a sufficient number of horrors have presented themselves in your standard cheaply-made jump-scare-driven horror schlock ripped from the trampled corpse of The Blair Witch Project (Paranormal Activity 9: We Used A Webcam For This One Because Cyber-Ghosts Or Whatever is my personal favorite), the protagonists would drop the camera and get the hell out of there. This is tackled admirably by the excellent sketch video "Hell No", which takes "What if horror protagonists acted like normal humans" as its premise and by that premise the only way the found-footage conceit can play out is the way they stage it: By having the cameraman stop filming when monsters show up. To do anything else is to have a protagonist so oblivious to the horror that surrounds them that it strains suspension of disbelief to the breaking point; either your hero is phenomenally dense… or they're not a hero at all.
Which, in turn, brings us to "Intrusion". For how simple the "guy filming the video is actually a madman" premise is I don't actually think I've seen it before; it's a wonderful inversion of the usual script, in that every other found-footage thing out there has programmed you into assuming that the person behind the camera is the hero. Of course, one of the major appeals of found-footage is that it lets the viewer "be" the protagonist of the story in a way that traditional third-person-shot narratives don't; we can be scared for Jamie Lee Curtis in Halloween but when the camera treats you to a first-person view of a dimly-lit hallway where someone or something is lurking, it lets us experience a more vicarious scare - you're being scared, not the character. So when "Intrusion" reveals its unreliable narrator, it shocks us into remembering that there is someone holding the camera who we've been implicitly identifying with for no real reason - apart from the fact that they're the one with the camera.
Upon rewatching "Intrusion" with knowledge of the twist ending, the opening moments take on a new and much more subtly horrifying significance; hairspray and women's deodorant on the end table, pink-colored wallpaper, and a strange lump in the middle of the bed are all clearly visible in the bedroom - but only briefly. This highlights one of the other main strengths of found-footage: Its ability to hide crucial visual information. If the short was filmed conventionally, it would have either been stunningly obvious that the cameraman was in a woman's bedroom with her corpse on the bed or it would have to be edited to such a degree that even on a rewatch it would be difficult to notice. But since our view of this world is given via shaky, quick-moving camera, the video can present all the damning evidence right to our face and know that we won't actually notice it the first time around. Of course, this is aided by the immediate identification of the cameraman as the hero; because we're told of the supposed intruder, we're concentrating more on that then on trying to disprove the cameraman's story. And that's the true brilliance of "Intrusion": It uses found-footage not as a crutch for lame shocks but as a method to subvert the genre with its own mechanics, to trick the viewer with your own knowledge of how these scenarios are supposed to play out.