Mustis may also refer to the ancient Roman city of Musti (Tunisia).Mustis is the pseudonym of Øyvind Johan Mustaparta (born 10 September 1979), a Norwegian keyboardist best known for his work in the symphonic black metal band Dimmu Borgir, as well as the black/thrash metal band Susperia. Mustis joined Dimmu Borgir in 1998 and has contributed to the further progression of their ambient, atmospherical, symphonic sound.