School of Horror (2007)

Aspiring filmmaker Rocky Horror (Robert Baldassari) devises a dangerous plan to create a surefire terror hit when he lures several film school classmates to a haunted tavern, hoping to capture footage of them being attacked by a legendary monster. But when the creature finally appears, Rocky and his fellow students realize that the blood and corpses are real, not special effects, and that the action may not stop when the director yells "cut."

Unfortunately the movie School of Horror is not yet available on HBO Max.