He credits Marble Hornets, Everyman HYBRID, and Tribe Twelve in the credits of the Concrete Giraffes video. If you do decide to watch these series I suggest starting with Marble Hornets as they assume the person watching does not know what Slender Man is. Also, HYBRID and Tribe Twelve have a tie in at some point, so I dunno, watch them both few videos here, few videos there. Those are the three big vblogs on Slender man, DarkHarvest00 is another I watch.