Anyways, be it as it is, Khadgar is not a warlock. Tirion is a paladin, and Thrall is a shaman.
This can not be a Warlock item
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None of you is right, since Guldan is the endboss of the second Legion raid, like Blackhand was in BRF, and not yet dead / killed when you are obtaining your artifact.
But also, there is the MU, dead Guldan, hmm.