People have been throwin' around all sorts of rumors.
Some have said it's a giant lion, because that's what the dude says at one point, though it's not totally clear.
Some even say it's Satan.
But what I know for sure is that the whole movie is going to be shot from the perspective of people with camcorders at parties and such. Just average dudes.
And maybe slusho.jp is part of an ARG.