At the summit of the Spire, you will confront The Architect, a high-ranking lieutenant to the Antagonist who masters necrotic and barrier magic. To succeed in this encounter, you must prioritize breaking his Frost Barrier using Lucanis and his "Eviscerate" ability, or Neve for her superior crowd control. The Architect is particularly weak to Necrotic damage but resistant to Cold, so equip gear that enhances your physical impact or blight-based spells.
The fight revolves around managing his "Abyssal Maw" cast, which must be interrupted using a Shield Toss or a high-stagger ability like Bellara’s "Replenishing Strike" to prevent massive AoE damage. When he retreats to the central platform to summon waves of Venatori Zealots, use Taunt abilities to keep the mobs grouped and focus on the casters first. Defeating The Architect clears the Spire and reveals a critical weakness in the antagonist's grand scheme.