The Ancient Shadowmoon Spirit has used you as a pawn! Now that you have collected the items he required, he has revealed himself to be Teron Gorefiend. To break free of his possession, you must do his bidding and slay Karsius the Ancient Watcher. If you succeed, return to Zorus the Judicator at Wildhammer Stronghold.
With Gorefiend's items restored, there is but one last piece to this puzzle: A host.
<The ancient shadowmoon spirit's lips curl up to form a wicked grin.>
Surely you did not believe the fairy tale that I told you. The Altar of Shadows is my prison. Without your help, I would have been stuck here for all eternity. Now, I will take over your body and you will destroy my captors and break these bonds. Refuse and we will both be stuck here forever.
Teron Gorefiend will be free!