Occultus never recorded, with MAYHEM, what your hearing is a bad recording of DEAD...

What you hear is Occultus who added vocals to Mayhem instrumental tracks.

Indeed vocals was added many years later, according to what can be read on this informative blog: http://pelleohlinmorbidmayhem.blogspot.it/

Incorrect. This is a rough mix of two tracks from DMDS with vocals overdubbed by Occultus sometime after the year 2000 (probably after 2004), making it one of the few truly interesting Mayhem bootlegs released during the past 15 years or so. Occultus even has a copy himself. The info on the artwork is incorrect, though - as you would expect from a greek-produced bootleg. The sound is great, however. If you can find one (at a reasonable price), I recommend that you buy it.

Some people from Greece, said to me that they pay Occultus to sing and record this 7ep !!!