A terrifying internet meme comes to life and turns out to basically be if The Ring was about incredibly annoying teenagers. Also, instead of being a creepy background figure, Slender Man has turned into basically a mean tree spirit that will straight-up choke a bitch.
System Mastery 
Re: “Did Red Letter Media Invent Slenderman” starts off with them running down the origins of Slenderman on Something Awful. They segue into discussing some odd similarities to a movie they made years ago, but they also acknowledge it’s all just a big coincidence.
I don’t know if you checked out Red Letter Media’s Half in the Bag review for this movie, but they talk about a bunch of stuff that was in the trailer but not the movie itself. One of them was a part cut from the science class scene where a girl does indeed stab herself in the eye with a scalpel. (When you mentioned that this didn’t happen, I was puzzled because I remembered seeing this in the trailer.) Another thing is apparently a bit of resolution with the boyfriend subplot since it appears to be a shot of him taking a dive off a bridge.
They also make mention in the beginning of the “Did Red Letter Media’s Invent Slender Man?” video, and Jay says, “Spoilers: we didn’t.” (I thought that was funny.)