To obtain this achievement, you will need the add, which can be found in the Terrace Gardens near where patrols, with two Celestial Acolytes channeling it. After clearing a path from the add to Star Augur Etraeus, the Nether Elemental should be pulled (by first pulling the other adds) to the boss, and then beginning the encounter.
As the different phases of the fight progress, the Nether Elemental will transform and gain increased health. When the final phase is reached, it will become the Well-Traveled Nether Elemental required for the achievement, which can then be killed before defeating the boss.
- Patch 7.0.3 (2016-07-19): Added.