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.$B$BThen, bring the gem to Nimboya.$B$BYenniku dwells with Zanzil the Outcast, at the Ruins of Aboraz, along the Crystal Shore on the distant Cape of Stranglethorn.