Xy Never, Ever Marks the Spot.

Enter the Sepulcher of the First Ones and engage Artificer Xy'mox. Three platforms in the encounter area each hold an artifact that spawns at specific health thresholds: one on the pull, one at 75%, and one at 50% while the boss is immune.

Assign dedicated players to collect each artifact as it spawns. Only one player needs to interact with each artifact, but the debuff it applies transfers to all players. Demon Hunters are recommended for this role due to their mobility, as a movement ability is required to reach each platform.

The three debuffs applied are Unstable Ephemera (a scaling damage-over-time effect), Crippling Ephemera (a 30% movement speed reduction), and Enfeebling Ephemera (a 25% maximum health reduction). All three must be active on every player when Xy'mox dies.

Do not use any ability that removes movement speed reductions while Crippling Ephemera is active, as this will remove that debuff and fail the achievement. Abilities confirmed to cause failure include Freedom, Bladestorm, Posthaste, and Druid Shapeshifting. As of the June 6 hotfix, Blizzard fixed an issue where Crippling Ephemera could be prematurely removed, so this behavior may now be more forgiving than it previously was.

With all three debuffs on every player, push Xy'mox to zero health. Dying during the fight does not remove the debuffs, so the achievement is not lost if a player dies as long as they still carry all three when the boss is defeated.