So on black phase there are diff. types of mobs - some of them are Maw of Go'rath (smallest hitpoints claw)
they cast instant cast Black Blood Eruption - Spell - World of Warcraft
and in spite of the fact that they have no mana - it can be copied by simulacrum Dark Simulacrum - Spell - World of Warcraft
in tank after 3 shadow phases every spell 300k damage+