Guide
How the kit works
Start with Nightrider to summon Oz. His arrival deals Electro damage in a small area, and he then attacks nearby enemies. Hold the skill to choose where he appears; press it again while he is present to bring him back to Fischl.
Switch to a teammate and trigger Electro-related reactions. Undone Be Thy Sinful Hex strikes an opponent for Electro damage equal to 80% of Fischl's ATK when your active character triggers one while Oz is on the field.
Use Midnight Phantasmagoria to move quickly through nearby enemies in Oz's form. Each enemy can be struck once during the ability. Oz remains afterward, and if he was already present, his duration resets.
Bolts of Downfall (NA) includes a fully charged Electro Aimed Shot. With Stellar Predator, hitting Oz with that shot causes an area Electro strike worth 152.7% of the arrow's damage. It is an option when Fischl is on field, though her off-field setup does not need her to aim at him.
Build and why
For off-field damage, use four pieces of Golden Troupe. Its two-piece bonus gives 20% Elemental Skill DMG, and the four-piece adds 25%. It gives another 25% while Fischl is off field, which ends 2 seconds after she takes the field. These bonuses suit Oz's skill damage.
For team support, consider four pieces of Celestial Gift. After Fischl completes Witch's Homework and uses her skill, nearby party members gain 20% Electro DMG Bonus. With Hexerei: Secret Rite, the upgraded effect instead gives 40% bonuses for Electro and the active character's element; matching elements do not stack.
Four pieces of A Day Carved From Rising Winds are another damage option. The set gives ATK, and after a hit its effect adds 25% ATK for 6 seconds. Completing Witch's Homework upgrades that effect to include 20% CRIT Rate. For a mixed set, two pieces each of Golden Troupe and Thundering Fury give Skill DMG and Electro DMG Bonus.
On sands, choose ATK Percentage, Elemental Mastery or Energy Recharge. Use Electro DMG Bonus or ATK Percentage on the goblet, and CRIT Rate or CRIT DMG on the circlet. Look for CRIT Rate and CRIT DMG in substats first, followed by ATK Percentage, Elemental Mastery and Energy Recharge.
The Daybreak Chronicles is a strong Bow for damage: its Normal Attack, Skill and Burst bonuses rise when the corresponding attack type hits. Polar Star gives 12% Skill and Burst DMG and can build ATK stacks from different attack types. The Stringless gives 24% Skill and Burst DMG, directly strengthening Oz's skill damage.
Leveling priority
For an off-field build, a sensible order is Nightrider first, then Midnight Phantasmagoria, then Bolts of Downfall (NA). Oz attacks through the skill, while the Burst also deals damage and refreshes his presence. Normal Attacks are less important if Fischl rarely stays on field.
For maximum ascension, you need 420,000 Mora, 168 Small Lamp Grass, 46 Lightning Prism, 1 Vajrada Amethyst Sliver, 9 Vajrada Amethyst Fragment, 9 Vajrada Amethyst Chunk and 6 Vajrada Amethyst Gemstone. You also need 18 Firm Arrowhead, 30 Sharp Arrowhead and 36 Weathered Arrowhead.
To max all three talents, gather 4,957,500 Mora, 9 Teachings of Ballad, 63 Guide to Ballad, 114 Philosophies of Ballad, 3 Crown of Insight and 18 Spirit Locket of Boreas. The talents also need 18 Firm Arrowhead, 66 Sharp Arrowhead and 93 Weathered Arrowhead.
Constellations worth it
C6 is the biggest upgrade to Oz's off-field role. It extends his presence by 2 seconds and makes him perform coordinated Electro attacks with the active character, each dealing 30% of Fischl's ATK.
C1 is useful for a different playstyle: when Oz is absent, he fires a coordinated hit as Fischl uses a Normal Attack. That hit deals damage equal to 22% of her ATK, so it matters more if you keep Fischl on field.
C3 is worth considering for the three extra levels it gives Nightrider. C2 improves the skill's initial damage and area, while C4 adds Burst damage and heals Fischl when the ability ends. C5 raises the Burst level. You do not need to build around any of these effects, though constellations are unlocked in order on the way to C6.
Common mistakes
Do not forget to bring Oz back near the fight. If opponents move away from him, press Nightrider again while he is present to reposition him beside Fischl.
Do not spend the whole rotation firing charged shots just to trigger Stellar Predator if you want Fischl's off-field role. Switch to a teammate and use reactions while Oz is present instead.
Do not assume Midnight Phantasmagoria needs Oz to be absent. Using it while he is already on the field resets his duration. Also check your Energy Recharge if the Burst is not ready when you want it.
Do not treat C1 as an off-field coordinated attack: it requires Fischl to use Normal Attacks while Oz is absent. C6 has a separate coordinated attack that works with the active character while Oz is present.
