Archmage Lan'dalock in Dalaran wants you to return with the Idle Crown of Anub'arak. This quest may only be completed on Heroic difficulty.
The Scourged nerubians are a plague upon our forces.
While we are safe from them here, floating above the world, when we set foot upon the land below, it is always with the thought that the undead nerubians could burrow up from the depths of Azjol-Nerub and attack.
It's in the best interests of everyone if they are thrown into a state of disarray. Kill their former king, and major-domo to the Lich King, the crypt lord, Anub'arak.
Please bring me his crown... not that he wears it any longer.