There was this hilarious documentary on metal bands (death and black metal, specifically), where the singer/shouter had problems remembering the text. Something

There was this hilarious documentary on metal bands (death and black metal, specifically), where the singer/shouter had problems remembering the text. Something about satan, or was it? He also had to grow real long hair, to put it in front of his face during a gig. Because who wants to see a bald man at a metal festival?