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This item unlocks the hidden appearance called Fate's End for the Affliction warlock artifact,  Ulthalesh, the Deadwind Harvester.  It drops from Sataiel.  The process of summoning the demon is somewhat involved and it will take most players a number of days to complete step 2.

1. Acquire a  Grimoire of the First Necrolyte.  It drops from Eredar Supplicant in Faronaar (west of Illidari Stand), Val'sharah.
2. Now you start the quest The Grimoire of the First Necrolyte.  It requires collecting 13 x  Skull of the Executed from rare elite mobs from World Quests. These mobs will require a group in order to kill them.
3. Use the 13 skulls at Executioner's Altar in http:/beta.wowdb.com/zones/41-deadwind-pass to summon Sataiel.