In the movie The Wild Hunt, after a series of incidents occur with the girl that the shaman likes, they end up kidnapping her and make her wear the skull mask. After she puts on the skull mask she starts freaking out and runs off. They start following her, starting the Wild Hunt, but isntead of playing in game they actually start killing people.
Why did they start killing people? Being upset over what happened in a game seems like a rather silly issue to kill people over.