The source of Illidan Stormrage's fel orc army has been vanquished. The manufactory halts production of its grim product - at least for now. All that remains are a few trinkets and this severed head - a fitting trophy for a hero of the Horde.
Return Magtheridon's head to Nazgrel at Thrallmar.
This defeat is not only a blow to Illidan, <name>. The Legion too reels... A pit lord commander has been defeated. The siege of Hellfire Citadel now holds no purpose for the Burning Legion. All of their efforts will undoubtedly be turned upon the Black Temple.