Aul, the Crystal King — Complete PoE 3.27 Delve Boss Guide

Aul, the Crystal King, is one of the three major Delve bosses in Path of Exile. He rules the Frozen Hollow and Crystal King’s Throne biomes deep within the Azurite Mine. Unlike most bosses in the game, Aul is not encountered through maps or invitations — he appears only through Delve node generation, making him one of the rarest and most valuable bosses in the entire game.

In PoE 3.27, Aul gained renewed relevance because defeating him unlocks the Aul Bloodline Ascendancy, a secondary ascendancy class that enhances aura effects and defensive scaling. This makes him not only a source of valuable loot but also a progression milestone for players exploring the Bloodline system introduced in 3.27.

Aul is infamous for:

• High burst damage
• Deadly cold mechanics
• Clone attacks that can shotgun
• Arena‑wide slams
• A shield phase that punishes slow builds
• Scaling difficulty that becomes absurd at deep Delve depths

This guide will walk you through everything: mechanics, strategy, builds, defenses, loot, and how to defeat him even at extreme depths reliably.

1. Arena Layout & Fight Flow

The Crystal King’s arena is circular, with icy terrain and limited safe zones. The fight has three major phases:

• Phase 1 — Standard Combat
• Phase 2 — Shield Phase (Pylons)
• Phase 3 — Enrage / Final Phase

Each phase introduces new threats, and the fight becomes progressively more dangerous.

2. Phase‑by‑Phase Breakdown

Phase 1 — Standard Combat

This is where Aul cycles through his core abilities. Understanding these is essential because they repeat throughout the fight.

A. Icy Clones (Ice Images)

These clones are one of Aul’s signature mechanics.

• Aul summons mirror images that dash across the arena.
• Each clone deals heavy cold damage.
• They can shotgun, meaning multiple hits can overlap.
• At deep depths, a single clone can kill you.

How to survive:

• Keep moving in wide circles.
• Never stand in a straight line with Aul.
• Use movement skills to reposition between clone waves.

B. Crystal Slam

• Aul raises his weapon and slams the ground, creating a massive cold explosion.
• This is one of his highest damage attacks.
• At depth 600+, it is almost always lethal.

How to survive:

• Move perpendicular to Aul — not backward.
• Watch for the wind‑up animation.
• Use instant movement skills (Dash, Frostblink).

C. Cold Waves (Expanding Rings)

Aul sends out circular waves of cold energy.

• These expand outward from his position.
• They deal cold damage and can overlap.

How to survive:

• Dash through the wave rather than trying to outrun it.
• Maintain mid‑range distance to reduce overlap.

D. Bullet Hell Mode

The guide calls this “Bullet Death Mode”.

• Aul fires rapid projectiles in a rotating pattern.
• The farther you are, the harder it is to dodge.

How to survive:

• Stay close and circle him.
• Move with the rotation, not against it.

Phase 2 — Shield Phase (Pylons)

At around 50% HP, Aul becomes invulnerable and summons four crystal pylons.

Mechanics:

• Aul gains a massive shield.
• You must destroy all pylons to break it.
• Each pylon destroyed triggers a cold explosion.
• Aul continues using abilities during this phase.

Strategy:

• Destroy pylons quickly — slow builds struggle here.
• Move diagonally between pylons to avoid clone lines.
• Use flasks before each explosion.

This phase is the most dangerous for builds with low mobility or low burst damage.

Phase 3 — Enrage / Final Phase

Once the shield breaks, Aul becomes enraged.

He gains:

• Faster clone spawns
• More frequent slams
• Higher cold damage
• Faster movement
• Faster projectile rotation

This is the “finish the fight” moment.

Strategy:

• Save cooldowns for this phase.
• Stay close to reduce projectile spread.
• Keep circling — stopping is death.
• Burst him down before the arena becomes too chaotic.

3. Required Defenses

Aul is one of the most defense‑checking bosses in PoE. Here’s what you need.

A. Freeze Immunity (Mandatory)

Aul deals massive cold damage, and many attacks can freeze.

You must have:

• Flask immunity
• Purity of Elements
• Boots with freeze immunity
• Or a crafted mod

Without freeze immunity, you will die instantly.

B. Cold Resistance

Aim for:

• 75% cold resistance
• At least 30–40% overcap for curses

C. Physical Mitigation

Aul deals a mix of:

• Cold damage
• Physical damage
• Physical → Cold conversion

Use:

• Armour
• Endurance charges
• Fortify
• Taste of Hate
• Determination

D. Spell Suppression

Aul’s projectiles and clone hits count as spells.

Aim for:

• 100% spell suppression if possible
• At least 60% for mid‑depths

E. Mobility

Movement skills are essential:

• Dash
• Frostblink
• Flame Dash
• Whirling Blades

You must be able to reposition instantly.

4. Loot & Rewards

Aul is one of the most profitable bosses in the game.

A. Aul’s Uprising (Unique Amulet)

These amulets grant:

• A free aura
• Or powerful aura modifiers

Some variants are worth many Divine Orbs.

B. Aul Bloodline Ascendancy

Defeating Aul unlocks the Aul Bloodline, which enhances aura effects and defensive scaling.

This is a major progression milestone in 3.27.

C. Fossils & Resonators

Aul can drop:

• Frigid Fossils
• Dense Fossils
• Pristine Fossils
• 3‑socket and 4‑socket resonators

D. Crystal King Rare PoE Items

These have Delve‑exclusive modifiers.

5. Deep Delve Strategy

At deep depths, Aul becomes one of the hardest bosses in the game.

A. One‑Shot Prevention

You need:

• 90% all res (Purity stacking)
• 100% spell suppression
• 50%+ physical mitigation
• 20k+ armour
• 5k+ life or ES

B. Positioning

• Stay close to Aul.
• Circle clockwise or counterclockwise.
• Never stand still.

C. Build Recommendations

Strong builds include:

• Juggernaut Sunder
• Aura stackers
• Minion builds
• RF Juggernaut
• Toxic Rain Pathfinder

6. Summary Table