Heart of Corruption

Source
This item is a quest reward from Walking in Shadows.

How to obtain

 * 1) Get the two Nat Pagle books
 * 2) *Nat Pagle's Guide to Extreme Anglin' rarely drops off players in Alterac Valley battleground
 * 3) *A Thoroughly Read Copy of "Nat Pagle's Guide to Extreme Anglin'." can frequently be found in A Dusty Tome in Dire Maul
 * 4) Talk to Sister Elda with both books
 * 5) *Your spec must be Retribution for her to respond to your books
 * 6) *She will give you A Complete Copy of "Nat Pagle's Guide to Extreme Anglin'."
 * 7) Kill Nefarian in Blackwing Lair and loot Head of Nefarian
 * 8) *Do not complete the quest the head offers; it is unrelated and will consume the head, forcing you to wait until the next lockout for another head. If you happen to still have his head from an earlier kill, you can use that.
 * 9) Talk to Prince Tortheldrin in Dire Maul West with the new book and Nefarian's head
 * 10) *Do not kill Immol'thar or Tortheldrin will become hostile
 * Talk to Alexia Ironknife at Chillwind Camp in Western Plaguelands / : Talk to Bardu Sharpeye at The Bulwark in Tirisfal Glades
 * 1) Read Grand Inquisitor Isillien's Journal at Hearthglen in Western Plaguelands
 * 2) *Coordinates are in the same building as High Cleric Alphus
 * 3) Kill the Large Vile Slime next to Thondroril River in Western Plaguelands
 * 4) *Supposedly has a random spawn up to 30 hours, unpredictable due to phasing and server sharding. The slime can be tagged by multiple cross-faction players.
 * 5) Use Timolain's Phylactery and talk to Timolain the Accursed
 * 6) Fish up the Shard of Darkness from the Thondroril River
 * 7) *You may fish anywhere along the river, as long as your location says "Thondroril River"
 * 8) *Your fishing skill does not matter
 * 9) Talk to Lord Maxwell Tyrosus in your class hall with the shard to start Walking in Shadows
 * 10) Go to Acherus: The Ebon Hold above the Broken Shore to complete the quest and earn the hidden appearance

Trivia

 * The questline to obtain this item is a reference to the old speculations about obtaining Ashbringer in classic.