Guide
How the kit works
Start with Binary Form: Convergence and Division to enter Essential Transmutation. While transformed, use the Skill input again for one area Pyro hit and the Confirmation of Purity state. Use the Normal Attack input instead for three Pyro hits in front and the Denial of Darkness state. Both states last 30 seconds. Entering either state in combat restores Energy, once every 6 seconds.
Then cast Principle of Purity: As the Light Shifts. Confirmation gives you Dragon of White Flame, while Denial gives you Dragon of Dark Decay. Both Burst versions first deal three area Pyro hits. Without either special state, the Burst defaults to White Flame. The dragons' periodic attacks count as Elemental Burst damage.
White Flame can reduce Pyro RES and the RES of the corresponding element by 20% for 6 seconds when nearby party members trigger Burning, Overloaded, Pyro Swirl or Pyro Crystallize. Pyro or Dendro damage against a Burning enemy also triggers the effect. Dark Decay instead increases Durin's Vaporize and Melt damage by 40% each.
After the Burst, Durin gets 10 stacks for 20 seconds. A dragon's periodic hit consumes one stack to increase its damage by 3% of the original damage per 100 ATK, up to 75%. A hit on several enemies still consumes only one stack. Casting the Burst again resets the stacks.
Build and why
For a team-focused build, use four pieces of Celestial Gift. Its two-piece bonus gives 20% Energy Recharge. After Durin completes Witch's Homework, using his Skill gives nearby party members 20% Pyro DMG Bonus for 20 seconds. With Hexerei: Secret Rite active, that becomes a 40% bonus for both Pyro and the active character's element; the bonuses do not stack when those elements match.
For Durin's own damage, four pieces of A Day Carved From Rising Winds give ATK, and hits activate another 25% ATK for 6 seconds. Completing Witch's Homework adds 20% CRIT Rate to that effect. Noblesse Oblige is another team option: its four-piece effect gives the party 20% ATK for 12 seconds after the Burst. Emblem of Severed Fate is worth considering for Energy Recharge and Burst damage.
Choose ATK Percentage or Energy Recharge on the sands, Pyro DMG Bonus or ATK Percentage on the goblet, and CRIT DMG or CRIT Rate on the circlet. For substats, look for CRIT DMG, CRIT Rate, ATK Percentage and Energy Recharge, in that order. ATK helps the passive that boosts dragon hits, while Energy Recharge helps you prepare the Burst.
Athame Artis is the first weapon choice: it increases Burst CRIT DMG and grants ATK after a Burst hit, including an ATK bonus for nearby active teammates. Freedom-Sworn is another option if Durin triggers reactions to collect its Sigils. Primordial Jade Cutter gives an ATK bonus based on the wielder's Max HP. Favonius Sword is worth considering when the team needs particles from CRIT hits.
Leveling priority
A sensible leveling order is Elemental Burst first, then Elemental Skill, then Normal Attack. Both dragons deal Burst damage, while the Skill gives you the hits used to select a form. Ordinary Normal Attacks are less central if you switch Durin out after setting up.
For maximum ascension, gather 420,000 Mora, 168 Frostlamp Flower, 1 Agnidus Agate Sliver, 9 Agnidus Agate Fragment, 9 Agnidus Agate Chunk, 6 Agnidus Agate Gemstone, 18 Tattered Warrant, 30 Immaculate Warrant, 36 Frost-Etched Warrant and 46 Cyclic Military Kuuvahki Core.
For all three talents at maximum level, you need 4,957,500 Mora, 9 Teachings of Ballad, 63 Guide to Ballad, 114 Philosophies of Ballad, 3 Crown of Insight, 18 Tattered Warrant, 66 Immaculate Warrant, 93 Frost-Etched Warrant and 18 Eroded Sunfire. These talent costs are separate from the ascension materials.
Constellations worth it
Adamah's Redemption is the standout upgrade. After White Flame's Burst, other nearby party members each get 20 stacks for 20 seconds; eligible damage consumes a stack to add damage based on 60% of Durin's ATK. After Dark Decay's Burst, Durin gets 20 stacks instead, with two consumed per Burst damage trigger to add damage based on 150% of his ATK.
For later upgrades, Dual Birth is worth considering for its DEF effects. Durin's Burst damage ignores 30% DEF. White Flame hits also reduce enemy DEF by 30% for 6 seconds, while the Dark Decay Burst and dragon ignore another 40% DEF.
Unground Visions is another useful option for the team: for 20 seconds after the Burst, the listed reactions or Pyro or Dendro damage against a Burning enemy can give nearby party members 50% Pyro DMG Bonus and 50% bonus for the corresponding element for 6 seconds. C3 and C5 raise talent levels rather than adding new effects, so you can leave them unpursued if those level gains are not your goal.
Common mistakes
Don't pick the form by accident. After entering Essential Transmutation, the Skill input selects White Flame's state and the Normal Attack input selects Dark Decay's state. Casting the Burst without a special state gives you White Flame.
Don't build around ordinary Normal Attack damage when you expect the dragon to do most of the work. Its periodic hits are Burst damage, even though one form is selected with the Normal Attack input. Give Durin enough Energy Recharge to use his Burst when you need it.
Don't assume White Flame's RES reduction is permanent: trigger the listed reactions or hit a Burning enemy with Pyro or Dendro to apply it again after its 6-second duration. For Dark Decay, make sure Durin is the one triggering Vaporize or Melt to benefit from his passive.
