The Arbiter of Ash
The Arbiter of Ash is the final boss awaiting you at POE2 Currency the end of Path of Exile 2. He's the ultimate challenge the endgame has to offer, with unforgiving mechanics and ruthless attacks. This pinnacle boss guide will show you how to reach him and tell you how to defeat him when you do.

How to reach The Arbiter of Ash
The Arbiter of Ash awaits you in his lair beneath The Burning Monolith, a landmark on the Atlas of Worlds that'll be just a few spaces away from your starting zone. However, to open the monolith, you'll need to collect Crisis Fragments from Citadels you'll find in the far reaches of the Atlas. Here are the three fragments you'll need.

Ancient Crisis Fragment: Gained by defeating Count Geonor in an Iron Citadel
Faded Crisis Fragment: Gained by defeating Jamanra the Abomination in a Copper Citadel.
Weathered Crisis Fragment: Gained by defeating Doryani, Royal Thaumaturge in a Stone Citadel.
When you have all three, insert them into the door at the Burning Monolith to gain access to The Arbiter of Ash's underground lair.

How to beat The Arbiter of Ash
The Arbiter of Ash is an incredibly unforgiving boss, with seven million health, many devastating attacks, and resistance to all the elements. You'll need to fine-tune your build and equipment to perfection if you hope to bring him down. Here are a few stats and abilities that can help you in this fight:

Movement Speed: Mobility is paramount in this fight as avoid the Arbiter's many area attacks requires getting to small safe zones in very little time.
Maximum Life and Energy Shield: It is possible to tank some of the Arbiter's attacks, so having a large effective life pool will come in handy in case you get caught in them
Acrobatics: This notable passive skill enables you to evade any attack, including the Arbiter's many one-shot area effects.
Dodge Roll Distance: The Surefooted Sigil is an amulet that can add one meter to your dodge roll distance, providing a much-needed boost to your mobility.
Maximum Fire Resistance: Most of the Arbiter's attacks are fire-based, so increasing your resistance beyond the normal 75% cap can help you mitigate even more of the damage.

The fight begins with the Arbiter firing a beam of fire right down the center of the circular platform. If you flank him, you'll have plenty of time to get in some attacks, putting a nice dent in his life at the beginning of the fight. He'll then begin attacking with various fire projectiles, some of which will skitter around the battlefield.

One of the Arbiter's attacks begins with him dashing around the battlefield, summoning firebombs that will slowly descend toward the platform. You need to move into the circle underneath each one as they fall. After one explodes, move to the next and so on.

When he gets to about 55% health, the Arbiter will pull his sword from the center of the platform. Then the real fun begins... He'll take on new, much more devastating attacks that are tricky to avoid.

He'll open this second phase with a new twist on the firebomb attack in which he'll summon a firebomb but fill the safe area with a wide beam of fire that will one-shot you if you're caught in it. You have the tiniest window of time to jump into the safe area before the bomb explodes. Then, dodge out of it quickly before the Arbiter follows it up with a slam attack that won't necessarily one-shot you but can obliterate your life.

Next, he'll summon huge waves of fire that leave only a straight lane of safety that's marked with two blue lines. You must get into that lane before the waves burst to avoid being one-shotted. He'll do this several times, alternating the direction of the waves. They're always barely enough apart for you to get to the safe area in time. Hence the dodge roll distance and movement speed buffs suggested above that'll help you cover the distance a little faster.

If you make it through those attacks, the Arbiter will summon two orbs, one blue and one purple. He'll pierce the blue one to cover the entire platform in frost. Then he'll continue his attacks while you're chilled by the cold. To get rid of it, walk over the purple orb, which will explode and banish the ice from the platform.

Ultimately, the keys to defeating The Arbiter of Ash are mobility, damage output, and practice. It's extremely unlikely that you'll take him down on your first try, as the timing of his attacks is so unforgiving. When you are accustomed to the patterns, you'll need the mobility it takes to keep up with them and the damage output needed to bring him down when you have an opportunity to attack.

The Arbiter of Ash rewards
When you do finally defeat The Arbiter of Ash, he'll drop a Book of buy POE 2 Currency Knowledge for his part of the passive skill tree along with some randomized loot.