Heart of Y'Shaarj
The Heart of Y'Shaarj, a diseased, icy mass of flesh seething with Void energies, is the actual heart of the deceased Old God, . When Y'Shaarj was torn apart by the titan , parts of the Old God's enormous body scattered across the landscape, and its monstrous heart was the largest part of it that remained intact. When was on his way to Uldum to install the Forge of Origination, he came across the Heart of Y'Shaarj and decided to seal it in a vault below the Vale of Eternal Blossoms. Ra's hope was that studying the heart would help the titan-forged gain a better understanding of the Old Gods and the Void. After creating the vault, Ra charged his mogu followers with watching over the chamber and the surrounding lands before continuing west.
During the Invasion of Pandaria, a goblin excavation unearthed the ancient vault, and the Heart was claimed for the Horde by . The Heart was then revived by , using the power of the magic pools of the Vale of Eternal Blossoms, unleashing the and corrupting most of the Vale in the process. It was later taken to Orgrimmar's Underhold, where it was mounted within Garrosh Hellscream's Inner Sanctum.
The Klaxxi allied themselves with Garrosh and his True Horde as a result of the Heart's presence, and it granted Garrosh visions of conquest. The mad Warchief also gained the ability to wield and manipulate its Void energies, infusing Malkorok with them, as well as abandoning Gorehowl in favour of a replica forged with the power of the Heart itself.
When the adventurers spear-heading the Siege of Orgrimmar reached the Inner Sanctum, Garrosh and the Heart of Y'Shaarj engaged them in what could be described as a tag team; alternating between Garrosh fighting them within his command chamber, and the Heart tormenting them in one of its twisted pocket dimensions. As the adventurers neared victory, Garrosh absorbed all of the Heart's power in a last-ditch move that transformed him into an avatar of Y'Shaarj. When even this monstrous form was defeated, the last power of Y'Shaarj drained away and left behind nothing but a Fading Breath that soon vanished as well.