Kill It With Fire!

When you enter the 'spirit world' at 50%, a Dark Hatchling will spawn. Every few seconds, a soul fragment will spawn that channels a heal on the Dark Hatchling. Let 3 spawn, then move them into the flame patches transforming them into Burning Souls. Kill them and then kill the boss to earn your Achievement!

Ok, everyone is making this WAY more complicated than it should be. Here are the steps to complete this:

1. During phase 1, a red phoenix will spawn. It leaves fire on the ground. Make sure a single fire spot is on the ground before damaging the boss to 50%.
2. During phase 2, a purple phoenix will spawn. It will spawn copies of yourself named Soul Fragment which will walk toward you. Position yourself between the phoenix and the fire that was spawned in Phase 1, the name of the Soul Fragment will change to Burning Fragment.
3. Kill 3 Burning Fragments. Done, achievement earned.

"Of course you should fight fire with fire. You should fight everything with fire."
-Jaya Ballard, task mage