Mithrix is found on Commencement, the final stage. To reach it, use the Primordial Teleporter on Stage 5 (Sky Meadow or Helminth Hatchery) rather than looping. Once on Commencement, charge any 4 of the 4-7 Pillars scattered across the stage, then use the launch pad to reach the arena. Walk inside the barrier to begin the fight.
It is possible to skip charging Pillars entirely using movement skills or items. Loader's grapple hook, Eccentric Vase, and several mobility combinations can reach the arena directly. In multiplayer all players must enter the arena barrier to start the fight.
Mithrix has a unique passive in Phases 1 and 3 that punishes burst damage. Every time he takes damage, he gains temporary armor equal to 30 armor per 1% of max HP dealt in that hit. This caps at 400 armor and decays at 40 per second.
Sustained consistent damage is far more effective than burst. Fire at a steady rate and allow the armor to decay between hits rather than dumping everything at once. Acrid's poison (% max HP) and sustained-fire survivors like Huntress and Railgunner (with controlled fire rate) handle this mechanic best. Abilities that deal many small hits over time also bypass the worst of it.
The fight is divided into four phases. Adaptive Armor is only active in Phases 1 and 3.
When Phase 3 ends, Mithrix walks to the center of the arena and becomes invulnerable while stealing all player items except equipment. He gains visible colored spikes (white for Common, green for Uncommon, red for Legendary). He slows significantly and switches almost entirely to tracking Needle Barrage.
Items are returned progressively as you deal damage. The more damage you deal, the faster you recover your build. A single Royal Capacitor can return roughly half your items in one hit. Phase 4 Mithrix is weaker than he looks because without full items your DPS is just lower and feels slower.
Phase 4 Mithrix is significantly slower and almost exclusively fires needles. Strafe constantly and keep shooting. The fight ends when his HP hits zero - all Chimeras die and the escape sequence begins. You do not need to reclaim all items before he dies.
20% bonus damage to bosses. When Mithrix steals them in Phase 4 he cannot use them against you since you are not a boss. Free damage advantage every phase.
When Mithrix steals Shaped Glass in Phase 4, his max HP is halved per stack. High risk but Phase 4 becomes extremely short. Works best if you can survive without it.
Extra jumps and sprint jump distance make Shock Wave rings and Big Spinny pillars much easier to dodge. Mobility items are highly valuable throughout all four phases.
Spare Drone Parts and Empathy Cores in Phase 4 can cause Mithrix to hit your own minions, triggering AtG missiles and Tesla Coil procs that kill you. Avoid giving him these.
Survivors with mobility for dodging, sustained fire for adaptive armor, and high single-target DPS perform best. Adaptive armor heavily punishes one-shot burst strategies in Phases 1 and 3.
Grapple hook mobility makes Shock Wave and Big Spinny trivial to dodge. Charged Gauntlet does massive burst but adaptive armor punishes pure burst - use sustained hits. Barrier generation from every hit provides significant tankiness in Phase 3. Strong across all four phases.
Highest single-target DPS, but adaptive armor requires controlled fire rate. Shoot one high-damage shot, wait for armor to decay, repeat. XQR Smart Round System locks on through his mobility. Phase 4 needles are easy to sidestep while sniping.
Defensive Microbots passively shoot down Needle Barrage projectiles, removing the primary ranged threat in Phases 1, 3, and 4. Diablo Strike burst from orbit. Shock Beacons stun-lock the Chimera Interlude. Strong across all phases.
Poison ignores adaptive armor since it deals % max HP damage. Acrid's poison continues ticking regardless of armor state, making him one of the best choices for bypassing the adaptive armor mechanic entirely. Mobility keeps him safe from hammers.
Snap Freeze execute is powerful on Chimeras in Phase 2. Ion Surge flight makes Big Spinny in Phase 3 much easier to dodge. Burst damage is punished by adaptive armor but Plasma Bolt sustained fire works well. Can skip Pillars of Commencement with Ion Surge for pillar skips.
Auto-aim fires constantly which rapidly stacks adaptive armor on Mithrix between hits. Must manually control fire rate or the armor mechanic negates most of her DPS. Laser Glaive multi-hit also stacks adaptive armor fast. Strong mobility is a major asset.
Heresy items cannot be stolen in Phase 4, so her full kit persists throughout the fight. Hungering Gaze continuous fire stacks adaptive armor quickly - needs fire rate control. Ruin detonation does not stack adaptive armor until detonation, making it an ideal burst tool. The constant HP drain is manageable if Shadowfade is used on cooldown.
Use the Primordial Teleporter on Stage 5 (Sky Meadow) instead of looping. Charge 4 Pillars across Commencement, use the launch pad to reach the arena, then walk inside the barrier. All players must enter the arena in multiplayer.
In Phases 1 and 3, Mithrix gains temporary armor equal to 30 armor per 1% of max HP dealt by any single hit. This caps at 400 and decays at 40 per second. Sustained lower-damage hits are more effective than trying to burst him down.
Mithrix steals all your items (except equipment and certain items like Heresy items). He becomes slower and primarily fires tracking needles. Dealing damage progressively returns your items. The fight ends when his HP reaches zero.
Yes but it is very difficult. Dealing damage in the exact first frame of Phase 4 starting can stun-skip the item theft animation. This most commonly happens with proc chain damage like Kjaro's Band triggering right as Phase 4 begins.
Defeating Mithrix and successfully escaping Commencement completes the Washed Away challenge and permanently unlocks Captain. This works on any difficulty.
Big Spinny (officially also called Forbidden Pizza by a Gearbox Community Manager) is Phase 3's rotating flame pillar attack. After a Shock Wave, Mithrix creates 9 pillars that rotate and then deal 900% damage plus Cripple. Dodge sideways between pillars rather than jumping over them.
No. Heresy items (Visions, Hooks, Strides, Essence) cannot be stolen by Mithrix. This is why Heretic players keep their full kit throughout Phase 4 regardless of item stealing.
