Defeat Taloc in Uldir after activating all Orbs of Harmony on Normal Difficulty or higher.
To complete this achievement, you need to collect all 4 Orbs of Harmony during the Taloc boss fight. The orbs are found in the elevator shaft, and you can pick them up as the boss goes down during phase 2. The orbs are in random positions, and the ones you collect won’t reset if you wipe, unless you reset the instance.
An easier way to do it is to bring a Havoc Demon Hunter and get them to jump down while gliding and Fel Rushing to pick up all the orbs, and wait for you at the bottom. You can see an example of that in this clip.
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Full Guide: https://www.mmo-champion.com/content/8274-Glory-of-the-Uldir-Raider-Achievement-Guide