Archmage Lan'dalock in Dalaran wants you to return with the Faceless One's Withered Brain. This quest may only be completed on Heroic difficulty.
The nerubians of Ahn'kahet dug too deep during their attempt to escape the invasion of the Scourge. They got too close to the Old God under Northrend.
Rousing its awareness, the Old God sent its insane creatures against them, and the nerubians were caught between the proverbial rock and a hard place.
The leader of the Old Gods' forces, Herald Volazj is one of the nightmarish beings known as The Faceless. Put an end to him and bring me his withered brain.
Just please, try to keep your sanity.