"Diabolical Fullmoon Mysticism" is the band's first full length offering and features the two founding members Demonaz and Abbath as well as Armegedda beating the skins. The record is the band's first journey into the mythical realm of Blashyrkh. The drumming is used quite effectively to highlight the music and ranges from death-metal rhythms to an occasional foray into a very rock'n roll kind of sound. The traditional black metal blast beats make a careful entry on this record but are certainly not as prevalent as on later Immortal records. The guitar sound is not quite the wailing, hypnotic shriek that many of the old school Black Metal bands enthralled us with, rather it is more of a Death Metal sound, which is not at all surprising considering that the band members' first steps in music were in the Death Metal genre. The production is surprisingly crisp and clear for what was then quite an underground release. All of the instruments are clearly discernible although they do seem to be a bit overpowered by the vocals on occasion. "Diabolical Fullmoon Mysticism" is a classic release, which should be a part of any serious black metal collection. It lays a thick foundation for Immortal's exploration of the realm of Blashyrkh and manages to create a cold and grim atmosphere without overdoing it and with seemingly natural ease. It is not as fast as ferocious as the later releases but as said before this is more than made up for by the sheer coldness of the sound.