Guide
How the kit works
Hold Basic Attack: Silenced Shot to enter Sniper Stance and fire Electric shots. Continuous fire and the charged counter grant 25 Purge when they hit, up to 100. Trigger automatically evades an incoming attack while firing, once every 8 seconds. You can also move left, right or back; moving just before a hit triggers a Perfect Dodge and an automatic charged counter.
Release the button for a Finishing Move. If it hits, it triggers the previous squad member's Quick Assist, subject to a 25-second cooldown. Trigger is invulnerable during the charged counter and Finishing Move. Her regular Basic Attack: Cold-Bore Shot fires up to four shots: the first three deal Physical DMG and the fourth deals Electric DMG.
With Purge available, another character's Basic Attack, Dodge Counter, Special Attack, Dash Attack or Quick Assist can trigger Basic Attack: Harmonizing Shot. It costs 3 Purge and can trigger once every 3 seconds. A heavy hit from an EX Special Attack, Assist Follow-Up or Ultimate triggers Basic Attack: Harmonizing Shot - Tartarus instead, costing 5 Purge. Each of those skill types can trigger it twice within 20 seconds across the squad.
EX Special Attack: Flash Burial (Special) starts Coordinated Support on hit: for 8 seconds, another active character's attacks can trigger up to four Harmonizing Shots without Purge cost or cooldown restrictions. Ultimate: Underworld Requiem gives 12 seconds and up to six triggers. Re-entering the state extends it, up to 20 seconds and 10 triggers. Both skills also trigger the previous character's Quick Assist on hit.
Build and why
Use four pieces of Shadow Harmony with two pieces of Woodpecker Electro. Shadow Harmony increases Aftershock DMG by 15% from its two-piece effect. Its four-piece effect gives up to three stacks of 4% ATK and 4% CRIT Rate when matching-attribute Aftershocks or Dash Attacks hit. Woodpecker Electro adds 8% CRIT Rate.
King of the Summit is an alternative: its two-piece effect increases Daze by 6%, while four pieces give the squad 15% CRIT DMG after an EX Special Attack or Chain Attack. At 50% CRIT Rate, that squad bonus rises by another 15%. Shockstar Disco is another option for Impact and Daze from the listed attack types.
Choose CRIT Rate on disc 4, Electric DMG Bonus or Percent ATK on disc 5, and Impact on disc 6. For substats, look for CRIT Rate, then Percent ATK and CRIT DMG. Additional Ability: Silver Lantern's Gaze converts CRIT Rate above 40% into more Aftershock Daze when its squad condition is met, up to a 75% Daze increase.
Spectral Gaze is the first weapon choice. Electric Aftershocks reduce the target's DEF by 25% for 5 seconds, and off-field triggers can build up to three Impact stacks. The Restrained is next: hits build stacks that increase Basic Attack DMG and Daze. Ice-Jade Teapot is another choice, giving Impact stacks from Basic Attack hits and a squad DMG bonus at 15 stacks.
Leveling priority
Follow the game's order: Core Passive first, then the Basic Attack skill group, Special Attack, Chain Attack, Assist and finally Dodge. The passive improves the effect applied by Aftershocks; the Basic Attack group contains the sniper and Aftershock skills you use throughout the fight.
For maximum ascension, gather 800,000 Denny, 4 Basic Stun Certification Seal, 32 Advanced Stun Certification Seal and 30 Buster Certification Seal. For all skills, gather 2,905,000 Denny, 25 Basic Shock Chip, 75 Advanced Shock Chip, 250 Specialized Shock Chip, 5 Hamster Cage Pass, 9 Ferocious Grip and 60 Higher Dimensional Data: Mortal Cleave.
Mindscapes worth it
I would consider Sharpened Senses first: it adds 20% to the Stun DMG Multiplier increase, reduces the regular Harmonizing Shot cooldown to 2 seconds and improves Purge gain and capacity. "Ether Vision" is another useful step, with up to four stacks that each give the squad 6% CRIT DMG for 10 seconds.
Beyond the River of the Dead is a later damage option. Its Armor Break Rounds add Electric DMG to Sniper Stance hits, with more rounds gained as Purge is consumed. Concealment (M4) is worth considering for its extra damage and Daze after entering or extending Coordinated Support. If those effects are not your goal, you can stop earlier; M3 and M5 add skill levels rather than a new mechanic.
Common mistakes
Do not leave Trigger on the field firing after you have built the Purge you need. Switch to another character so their attacks can trigger her Aftershocks. Watch the Purge supply: outside Coordinated Support, those attacks consume it.
Do not ignore the team condition or stack CRIT Rate without checking the Daze cap. Also remember that the sniper Finishing Move's Quick Assist has its own 25-second limit, so it will not be available after every use.