The Arbiter of Ash

Overview

The Arbiter of Ash is the pinnacle boss of The Burning Monolith, inside the Fortress. This strategy is the regular version, not the Uber one. Every kill drops one guaranteed unique from a pool of six, and two of those uniques carry almost all the value. The fight is short, and you get unlimited respawn attempts, so a death costs you time but not your fragments.

Setup

One run consumes three fragments: a Weathered Crisis Fragment, a Faded Crisis Fragment and an Ancient Crisis Fragment. Take all three to the Burning Monolith and the encounter opens. Nothing else is consumed.

The Encounter

He is level 82 and deals physical and fire damage. Since patch 0.5.4 his elemental resistances are 30%, down from 75%.

Phase one is mostly ground avoidance. He covers the arena in red mist and then sets it alight, drops rings of flame seeds that explode everywhere outside the ring, and fires slow orbs that spray projectiles. During the gales there is a clear strip through the middle of the arena. Use it.

At 50% life he becomes immune for a moment, teleports to the centre, heals to full and swaps his sceptre for a sword. Phase two keeps everything above and adds two seeds at opposite ends of the arena. If he stabs the white seed, the floor chills you and slows you by 30%. If he stabs the purple one, the floor applies Blackflame, which stops all life and energy shield recovery for 20 seconds. That is what kills people. Bring fire resistance, a reliable way to move out of ground effects, and enough damage that you are not standing in Blackflame waiting to heal.

How These Numbers Were Calculated

Nobody ran this a hundred times and wrote down the loot. The sample here is built from the drop rates published on the wiki, scaled to 100 kills: a 3% chance is counted three times, a guaranteed drop is counted on every kill, and expenses are one run's fragments multiplied by the same 100 runs.

The rates come from a sample of 235 regular kills spanning versions 0.3.0 to 0.5.0, so they are estimates and they predate some of the boss's rebalancing. Three of the uniques, Solus Ipse, Sine Aequo and Ab Aeterno, have no published rate at all. Their share was worked out from the fact that the guaranteed pool has to add up to exactly one drop per kill, then split using the Uber version's ratio between them. All three sell for close to nothing, so even a poor guess there barely moves the total.

The profit is concentrated. Prism of Belief drops on about 23 kills in 100 and accounts for roughly three quarters of the modelled income. Morior Invictus, at 48 in 100, accounts for most of the rest. Together they are about 99% of it. Expect short runs of kills to look nothing like the average. If Prism of Belief has not shown up in fifteen attempts, that is ordinary variance, not a broken strategy.