Assault on Blackwing Lair

Deeply inside the screaming heart of Blackrock Mountain, the black dragon Nefarian carried out twisted research using the blood of other dragonflights. Focused on taking ownership of the whole location for his very own, he assembled the remainder of the Dark Horde, a criminal militia that adopted the demonic bloodlust from the old Horde. These darkly tainted orcs, trolls along with other races fought up against the Firelord Ragnaros as well as shadowy Dark Iron dwarves for power over the fiery mountain. Just before he was vanquished by courageous heroes, Nefarian developed the twisted chromatic dragons along with a legion of other aberrations within his bid to create a military strong enough to overpower Azeroth and carry on the legacy of  "Deathwing the Destroyer" his notoriously evil father.