The Arbiter of Ash is one of the most challenging bosses in Path of Exile 2-a true test of skill and preparation. It requires a lot of patience and precision, as the encounter has a lot of moving parts, particularly with the phases and attack patterns. Here's a breakdown of how to approach the fight based on your description:

How to Start the Arbiter of Ash Boss Fight

Unlocking the Burning Monolith:

You'll need Crisis Fragments from different bosses scattered across the Atlas of Worlds. These bosses drop the Fragments, which can be used to unlock the Burning Monolith. The Citadel dungeons where they spawn are random, so it might take some time to collect the right ones.

Tip: Don't rush this stage. Farm for your materials, and make sure your build is optimized for endgame content. Craft or trade for any gear upgrades to ensure you're in the best shape possible for the fight.

Phase One

Initial Setup: At the start, you have some time to prep your buffs as the boss introduces itself with a large explosion. Then, the fire beam will sweep the arena-dodge it and move behind the Arbiter to start your attack rotation.

Dangerous Attacks: Keep an eye out for the fireball pairs, which will follow you around and shoot bolts at intervals. Their movement can be predictable, so you can stay mobile to avoid them.

The explosion rings (large fiery circles) are another major threat. Run to the center to avoid the burst when you see them form.

Insta-Kill Mechanics: When you notice fiery streaks across the battlefield, the Arbiter will try to set up an Insta-kill. Install the blue section in the pattern and stand in it to survive.

Overall Phase One Strategy: Focus on dodging the attacks while dealing consistent damage. Save your burst damage for when the Arbiter is at about 50% HP to trigger Phase Two.

Phase Two

Changes in the Fight: Once the Arbiter draws his sword, things get much quicker and deadlier. His fire beam now spans a wider area, and he's more aggressive with his melee combos. Keep dodging, as these combos are fast and can easily overwhelm you.

Elemental Orbs: The Arbiter summons blue and purple orbs in this phase. The blue orb creates Frozen Ground, which slows and damages you, making it harder to move. The purple orb neutralizes the ice, so you need to touch it to keep moving freely.

Increased Difficulty: The main challenge here is how fast the Arbiter gets and the overlapping AoE attacks. Movement speed and armor will be essential to stay out of the danger zones. If you're able to tank some of the damage, it might make dodging a bit less punishing.

Tips for Success

High Movement Speed: Since dodging in Phase Two can be frantic, you'll want to be as fast as possible to stay ahead of the Arbiter's attacks.

Armored Build: Armor will help you withstand some of the AoE damage in the second phase, where the danger from overlapping attacks can be overwhelming.

Strong DPS: Ensure your build can dish out enough damage quickly during the pauses in attack sequences. Aim for high burst damage during those moments of safety.

Learn Telegraphs: The more you play through the encounter, the better you'll get at recognizing the attack telegraphs. The quicker you can react to them, the more likely you'll survive and succeed.

This is a boss that's going to take some practice to master, especially given how intense the overlapping mechanics are in Phase Two. If you've got Path of Exile 2 currency and Path of Exile 2 items, you're in a good position to trade for any specific gear upgrades or crafting materials to fine-tune your defenses and DPS output. Are you planning on adjusting your build for this fight, or are you already comfortable with a setup that you think will work?