The Legendary Evoker Weapon dropped for the first time on Mythic difficulty, but it can now drop on any difficulty after the Weekly Reset for NA and EU Regions.
When Liquid defeated Mythic Sarkareth for the first time earlier today, the first Cracked Titan Gem dropped! This seemed to mean that the Legendary Evoker weapon Nasz’uro, the Unbound Legacy could only drop from Mythic difficulty.