‘Sleepwulf’ refers to the Nordic gods Skoll and Hati, two wolves who continually hunt the sun and moon across the sky. Does this tell you anything about their music? Not necessarily no, but be aware that these Swedes (and one Scotsman) enjoy their mythologic worldbuilding, and extend it to the music which sounds like Sabbath and Jethro Tull jamming in some secluded woodland.