Shortly after the return of the Burning Legion, Priestess Tyrande and Archdruid Malfurion made a desperate journey down into the Barrow Deeps of the Druids of the Claw. These druids had been in hibernation, exploring the Emerald Dream where Ysera lives, but had nestled very close to the prison of Illidan. In the depths of the Barrow Deeps, at the entrance to the prison, Tyrande decided to free Illidan, allowing him to face the Burning Legion with his powers. Malfurion opposed this, and the two went in separate ways. Tyrande and a small cadre of Night Elf Sentinels fought their way to the cell containing Illidan and set him free.

Upon returning to the surface, Illidan led the Night Elves in destroying some of the dimensional gates, then disappeared. Illidan was soon led by (in the sense that he told him about the artifact to achieve his own goals without letting him know about the consequences) the Death Knight Arthas to find a powerful demon artifact, the Skull of Gul’dan, that the Burning Legion was using to corrupt and poison the Felwood forest. Illidan destroyed the artifact, absorbing the power and some of the memories of Gul’dan, and transforming him into a demi-demon; the transformation granted him wings and horns as well as new demonic powers. He then hunted down and killed Tichondrius, lord of the Nathrezim. Despite Illidan’s role in saving the forest, Malfurion was shocked that his brother had so totally given himself over to the quest for power and banished Illidan from Ashenvale. The fuming Illidan then stormed off leaving a burning trail in his wake.