Depends on what sort of mood I'm going for. Could be 80s rock (Skid Row, Def Leppard, Warrant, White Lion), power metal (the real dungeons and dragons, swords and shields stuff, like Manowar, Rhapsody, Kamelot, etc), death metal (Morbid Angel, Cannibal Corpse, Deicide, Immolation, Meshuggah, old Strapping Young Lad) if I want to get aggressive, and changes in speed and time signature are ok, if I need a continuous rhythm, then long sets of psytrance, hardcore, or techno are more what I'd use.

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