To understand Y'Shaarj, you must look back to the time before the return of the Titans, when the Old Gods made sport of their creation. Azeroth was that which they battened upon - they infested the world like parasites, drained its essence, forced its very elements to fight for their amusement. The mantid descend from the servitor races the Old Gods created to honor and adore them in their great wickedness. To quote the mantid:
Before your history began, our empire was vast. We shared this world with our sister kingdoms, Ahn'Qiraj and Azjol-Nerub.
Our Gods were many, and powerful. We mantid worshipped the seven heads of Y'shaarj.
Great was the Old One, and terrible was His wrath. He consumed hope and begat despair; He inhaled courage and breathed fear.
When the usurpers came - the ones you call "Titans" - Y'shaarj was destroyed.
His last terrible breath has haunted this land ever since, but the shadows he left behind are mere whispers of his former glory.
What we know of the history of Pandaria tells us that when they returned, the Titans raised a war host to do battle with the Old Gods, a host led by powerful beings and composed of stone warriors (using the resilient foundation of creation in a subterranean being matrix as we discovered in Uldaman) - each region of Azeroth seems to have had a slightly different version of these legions. In the region now known as Uldum, the Keepers created stone servants and in Ulduar the legacy of the Titans can be seen in the many watchers, the vrykul, earthen and giants. In what we now call Pandaria, one of these Titanic Watchers, Ra,(known by the mogu as Master Ra, or Ra-Den in their later language) led a legion of stone to protect one of the Titans precious life-cradles, a place known to us as the Vale of Eternal Blossoms.
During this time, the battle between Titan and Old God reached its climax. In the southern hemisphere, the dread seven headed monstrosity Y'Shaarj, the eater of hope, met a Titan in combat. And in the end, the world discovered why these potent forces had done their best to battle through proxies, why Y'Shaarj had sent winged legions to do battle with Ra-Den and his army of stone. The Old God died, and the Titan fell. In death, Y'Shaarj poured his terrible final breath forth onto the land, and from that act was born the hideous Sha. Each of the prime Sha is an echo of Y'Shaarj's many heads, and they infested the land drawing strength from the negative emotions of mortals.
And in this way Pandaria has never been free from Y'Shaarj. When the Emperor Shaohao purged himself of his doubt, hatred, anger, despair, violence and fear and imprisoned them in the land, he was conquering aspects of Y'Shaarj, but by not purging himself of his pride he ultimately failed, and it was the Sha of Pride that created the concealing mists that sheltered Pandaria from the effects of the Sundering - and which kept it, proud and isolated, to stagnate for 10,000 years while the rest of the world moved on without it. During the reign of the mogu, after Lei Shen had ascended to the throne as Thunder King and first Emperor, the Korune magicians created the Divine Bell, with which the anger and hatred and violence of mogu warriors could be enhanced while the doubt, fear and despair of their enemies could be magnified - made from the flesh of a maker, it drew upon darkest shadow - the shadow of Y'Shaarj itself, a being of shadow.
And in the very heart of the Vale of Eternal Blossoms, that cradle of life Ra=Den and his legions first marched to protect, the Titans buried an even more terrible artifact, for even in death Y'Shaarj reached out to corrupt and befoul the world. Y'Shaarj's malevolent heart, a thing of pure darkness which whispers foul promises and corruption, was imprisoned in a great vault and sealed away under the watch of Norushen, possibly a direct servant or lieutenant of Ra-Den. As to why the Titans chose to seal away the Heart of Y'Shaarj instead of destroying it, we don't know. Perhaps they couldn't destroy it, perhaps they feared to do so, or perhaps the Heart is in some way connected to the magical potency of the Vale's waters. But what we do know is as follows: Y'Shaarj, despite being dead, can still speak to others, can still tempt them to open its containment vessel, and once this has been done, Y'Shaarj can possess them. An insufficiently strong will is obliterated instantly, as the first fool who opened the Old God's prison discovered.
Now, going into patch 5.4, we know that the breaching of Y'Shaarj's prison seems to have drawn the Sha of Pride to the Vale, perhaps attempting to find and rejoin with the heart of Y'Shaarj. Meanwhile, Garrosh Hellscream has removed the heart to Orgrimmar, seeking to repeat his earlier experimentation with the Divine Bell but this time with a more pure source, for Y'Shaarj's power is that of all seven Sha combined. What's more, the fact that Y'Shaarj, despite its death, can communicate with others and the arrival of the Sha of Pride in the Vale upon its exposure implies that Y'Shaarj can still reach out to the larger world and that could be why it was sealed away underneath the Vale, to prevent its song from stirring the hearts of its followers. The Dread Wastes border the Vale - only the Serpent's Spine prevents the mantid from ranging further afield.
Worse, we know that the Klaxxi have sent their Paragons to Orgrimmar in patch 5.4, although we don't know why yet. Did Y'Shaarj call them? Is the heart that powerful, even in death? And will it be Garrosh Hellscream using it, or it using him? We are on the cusp of finding out the answers to these questions. Y'Shaarj slouches towards Orgrimmar.
While you don't need to have played the previous
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World of Warcraft, a little history goes a long way toward making the game a lot more fun. Dig into even more of the lore and history behind the
World of Warcraft in WoW Insider's Guide to Warcraft Lore