Proposed Fight Structure:

1. Phase 1 - Elias, Master of Diablo 4 Items the Triune

Classic spell-slinger arena with summon-heavy mechanics: ritual spikes erupting from the ground, homing blood sigils, waves of minor Triune cultists.

2. Phase 2 - Arena Shift

As players "defeat" him, Elias vanishes in a flash of blood magic and flees through a shattered gate. Players must chase him down a short gauntlet filled with exploding sigils and teleporting ambush enemies.

3. Phase 3 - Elias, Fallen Horadrim

Rage-fueled final form. Faster attacks, tri-directional blood wave walls, shadow clone illusions, and constant teleport spam. Think Duriel's relentless aggression, but mixed with Astaroth-style magical chaos.

Key Hooks:

No Lorath ally this time.
Faster animation speeds and HP scaling to rival Duriel's difficulty.
Mythic Unique loot table could feature Triune-themed caster pieces or curse-enhancing Necromancer loot.

Broader Gameplay Benefits

Breaks up monotony by adding badly needed boss diversity in the Greater tier.
Justifies more build experimentation, as players would need resistances/mechanics tuned to Elias, not just poison/physical for Duriel.
Injects fresh lore relevance into Season 9 without building a boss from scratch.
Gives Necromancer and caster fans a strong thematic opponent while expanding on buy Diablo 4 Items the Horadrim betrayal story.