Was Oystein "Euronymous" Aarseth a guitarist in the band or co-founder of the band Mayhem?
Parabellum (band):  According to writer Emilio Cuesta, Øystein "Euronymous" Aarseth—a musician associated with the early Norwegian black metal scene—has said Parabellum and Medellín's Reencarnación were both influential to his own band Mayhem.
i don't know