Filene/Strategy

Strengths

•  Whitefrost Whisper400% Water damage to a foe (Damage cap: ~630,000).
  Inflict 10% ATK Down (Stackable / Max: 40%)ATK is lowered (Stackable)
  Strength: 10% (Max: 40%)Base Accuracy: 100%Duration: 180 seconds, 10% DEF Down (Stackable / Max: 40%)DEF is lowered (Stackable)
  Strength: 10% (Max: 40%)Base Accuracy: 100%Duration: 180 seconds, and Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
  Base Accuracy: Guaranteed to land if the foe does not have 100% debuff resistance (10,000% base accuracy)Duration: 4 turnsLocal status effect. debuffs a foe with ATK Down (Stackable / Max: 40%)ATK is lowered (Stackable)
  and DEF Down (Stackable / Max: 40%)DEF is lowered (Stackable)
  - almost capping DEF Down plus ATK Down on its own - while also inflicting Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
  Local status effect.
  • The skill will be auto-cast whenever an ally casts a skill that inflicts GlaciateHP is lowered each turn / Multiattack rate is lowered
    or ColdcageCan't attack
    Local status effect thanks to  Your Final BreathActivate Whitefrost Whisper when an ally casts a skill that inflicts GlaciateHP is lowered each turn / Multiattack rate is lowered
    or ColdcageCan't attack
    Local status effect. (which can be triggered by using  Frigid Embrace6-hit, 100% Water damage to a foe (Damage cap: ~120,000 per hit).
    Inflict GlaciateHP is lowered each turn / Multiattack rate is lowered
    Strength: 9999Base Accuracy: 100%Duration: 3 turns and DelayReduce a foe's charge diamonds by 1
    Base Accuracy: 100%.). This causes the stackable debuffs to reach their max values much faster.
  • Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
    Local status effect can't be removed and will always land unless the foe has 100% debuff resistance, making it reliable even in longer fights.
•  Frigid Embrace6-hit, 100% Water damage to a foe (Damage cap: ~120,000 per hit).
  Inflict GlaciateHP is lowered each turn / Multiattack rate is lowered
  Strength: 9999Base Accuracy: 100%Duration: 3 turns and DelayReduce a foe's charge diamonds by 1
  Base Accuracy: 100%. also offers DelayReduce a foe's charge diamonds by 1
  on 6-turn cooldown.
•  Silvery SnowAll Water allies gain Silvery SnowWater ATK is boosted / Skill DMG is boosted / Maximum amount of skill DMG that can be dealt per hit is boosted (Can't be removed)
  Duration: 6 turns. boosts all allies' Water ATK, in conjunction with increase to skill damage and skill damage cap, making her suitable for skill-damage-based parties. Silvery SnowWater ATK is boosted / Skill DMG is boosted / Maximum amount of skill DMG that can be dealt per hit is boosted (Can't be removed)
  's duration extends by 2 turns after every charge attack she deals.
• She lowers damage taken by all allies from foes with Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
  Local status effect, thanks to  PermafrostReduce Water allies' damage taken from foes with Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
  Local status effect by 20%..

Weaknesses

• Despite being presented as skill-damage-based character, Silvery SnowWater ATK is boosted / Skill DMG is boosted / Maximum amount of skill DMG that can be dealt per hit is boosted (Can't be removed)
  has pitiable 6/12 turns uptime. This forces Filene to seek external supporting buffs in form of attack rate or charge bar/charge bar gain for more frequent charge attacks to prolong the buff's duration.
• Very scarce sources of skills inflicting GlaciateHP is lowered each turn / Multiattack rate is lowered
  and ColdcageCan't attack
  Local status effect in Water limit the auto-activating capability of her skill.

Skills that inflict Glaciate or Coldcage

• Aglovale:  Eiszapfen250%-300% Water damage to all foes (Damage cap: ~440,000).
  Inflict 20% Fire ATK DownFire ATK is lowered
  Strength: 20%Base Accuracy: 90%Duration: 180 seconds and ColdcageCan't attack
  Base Accuracy: 90%Verification needed. Duration: 2 turnsLocal status effect.
• Lily:  Frozen Gale150%-200% Water damage to all foes (Damage cap: ~420,000).
  Inflict GlaciateHP is lowered each turn / Multiattack rate is lowered
  Strength: 9999 DMG /Base Accuracy: 90%Duration: 3 turns.
  At level 75:
  Damage increased to 250%-350%.
  At level 100:
  Damage increased to 400%.
  Damage cap increased to ~500,000.
  GlaciateHP is lowered each turn / Multiattack rate is lowered
  Strength: 9999 DMG /Base Accuracy: 100%Duration: 3 turns success rate increased to 100%.
  Also inflict 10% ATK Down (Stackable / Max: 40%)ATK is lowered (Stackable)
  Strength: 10% (Max: 40%)Base Accuracy: 95%Duration: 180 seconds and 10% DEF Down (Stackable / Max: 40%)DEF is lowered (Stackable)
  Strength: 10% (Max: 40%)Base Accuracy: 95%Duration: 180 seconds.
  When exactly 2 races among main allies: Damage cap increased to ~600,000.
  When 3 or more races among main allies: Activates twice.
• Macula Marius:  Glacial TundraInflict 25% ATK DownATK is lowered
  Strength: 25%Base Accuracy: 100%Duration: 180 secondsStacking: Single, GravitySpecial attack max charge turn is extended
  Base Accuracy: 100%Duration: 180 seconds, and GlaciateHP is lowered each turn / Multiattack rate is lowered
  Strength: 9999 DMGBase Accuracy: 100%Duration: 3 turns on all foes.
• Runeslayer:  RuneweavingCall forth the power of the tetra-elements to cast a spell. - Freezing Shackles +

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  Water damage to a foe.

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  Water CircleA magic circle possessing the power of water (Max: 2 / Can't be removed)
  : Inflict ColdcageCan't attack
  Duration: 2 turnsLocal status effect. (Requires Water CircleA magic circle possessing the power of water (Max: 2 / Can't be removed)
  from Aquatic Blade +

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  Water damage to a foe and gain Water CircleA magic circle possessing the power of water (Max: 2 / Can't be removed)
  ..)

Skill Damage Boost

Having external source of skill damage boost increases her skill damage contribution, especially from  Whitefrost Whisper400% Water damage to a foe (Damage cap: ~630,000).
Inflict 10% ATK Down (Stackable / Max: 40%)ATK is lowered (Stackable)
Strength: 10% (Max: 40%)Base Accuracy: 100%Duration: 180 seconds, 10% DEF Down (Stackable / Max: 40%)DEF is lowered (Stackable)
Strength: 10% (Max: 40%)Base Accuracy: 100%Duration: 180 seconds, and Whitefrost WhisperTakes bonus DMG from Filene's charge attack (Can't be removed)
Base Accuracy: Guaranteed to land if the foe does not have 100% debuff resistance (10,000% base accuracy)Duration: 4 turnsLocal status effect. which auto-activates by casting skills inflicting GlaciateHP is lowered each turn / Multiattack rate is lowered
or ColdcageCan't attack
Local status effect. Some of the sources are:

• Clarion (4★): Cobalt ArtsBoost to Water allies' skill damage cap.
• Staff of Repudiation/ Staff of Renunciation (4★): β Revelation50% boost to skill DMG cap.
• Ultima Weapons
  • Ultima Sword
  • Ultima Dagger
  • Ultima Spear
  • Ultima Axe
  • Ultima Staff
  • Ultima Gun
  • Ultima Claw
  • Ultima Bow
  • Ultima Harp
  • Ultima Blade
  : Gauph Key β50% boost to skill DMG cap.

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  Does not need Filene to match Ultima Weapon type to take effect.