I have reshaped the Mind's Eye into a Soul Gem. Its purpose is twofold: you must use it to stun Yenniku, and once stunned place it upon his head to entrap his soul.
My suspicions that I spoke of earlier were correct: the spirits tell me that Yenniku dwells not with Zanzil the Outcast, but within the Ruins of Zul'Mamwe, to the southwest. Once you have freed Yenniku's spirit, return to Nimboya at Grom'gol.
You've done it! You freed Yenniku from the will of Zanzil and the tyranny of the Skullsplitter, and completed the mission I had thought was so hopeless. Zanzil still looms a threat in the Cape of Stranglethorn, but for now, I at least know that the soul of my chief's son is free.
Our tribe will remember your name in songs, <name>, and we will etch your tale in stone so that it will live forever.