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HeathcliffWild Hunt
When you get him to high SP, use his defense skill to have him mount 
Dullahan. His S2 and S3 will be buffed while he has it and he'll passively gain 1 stack of it per turn at the cost of losing some SP up to a max of 3 stacks. You'll want to use his S3-2 when he has 3 stacks and at as low SP as possible. If you have his S3, you can let him go down to -24 SP before he automatically loses the buff. Otherwise, you can use his counter even before reaching 3 stacks to force an S3-2 use if he still has 15+ SP.
His S3-2 is a minus coin skill that drops his SP by 15, then consumes Dullahan to increase its damage per stack. It inflicts more 
Sinking and has more damage bonuses than his regular S3. He then heals back to positive SP afterwards.
Builds 
Coffin whenever he kills an enemy or uses his S3, giving him passive 
Damage Up, speed, and 
Clash Power Up depending on the stacks. If his passive is active and an ally dies, he consumes 2 Coffin to revive them at 50% HP and 0 SP for 1 turn. They get Damage Up and Wuthering Heights/Edgar Family identities gain an additional 
Attack Power Up for that turn, but they immediately die afterwards. Every stack of Coffin also increases the damage either version of his S3 deals.
His S2 gains +1 atk weight for every 4 Coffin stacks and another +1 if he has Dullahan for up to +3 weight. It inflicts 
Impending Ruin which applies additional Sinking and 
Clash Power Down when enemies hit low SP or panic. Enemies without SP get a -10% chance to flip Heads.
Having 3 allies die forces him to mount Dullahan automatically.
3 +4
62 (+2)Clash: 4-19Damage: 6-46.5Atk Weight:Sinking, Clash Power +1
[On Use] Coin Power +1 for every 3 Sinking Count on target (max 2)
Sinking
5 +362 (+2)Clash: 5-23Damage: 15-87.19Atk Weight:Sinking on target (max 2)
[On Use] Atk Weight +1 for every 4 Coffin on self (max 2)
[On Use] If this unit has Dullahan, Atk Weight +1
[Attack End] If this unit has Dullahan, lose 10 SPSinkingSinkingImpending Ruin next turn
6 +665 (+5)Clash: 7-30Damage: 26.4-137.18Atk Weight:Dullahan, activate 'Lament, Mourn, and Despair' instead
[On Use] Coin Power +1 for every 3 Sinking on target (max 4)
Deal +12% damage for every Coffin on self (max 120%)
[On Use] Gain 1 Coffin
[Attack End] If this Skill attack kills the target, gain 2 CoffinSinking CountImpending Ruin, inflict +2 Sinking CountSinkingSinking on killed target/2) Sinking on 2 random enemies (max 5)
31 -1365 (+5)Clash: 10-39Damage: 117.11-305.9Atk Weight:Sinking on target (max 4)
[On Use] Deal more damage the further this unit's SP value is from 45 (+0.3% damage for every missing SP, max 21%)
Deal +10% damage for every Coffin on self (max 100%)
Deal +20% damage for every Dullahan on self (max 60%)
[On Use] Gain 2 Coffin
[Attack End] If this Skill attack kills the target, gain 3 Coffin
[Attack End] At less than 0 SP, heal 10 SP. When at less than 0 SP, heal more SP the further this unit's SP value is from 0 (heal 2 additional SP for every missing SP; max 50)
[Turn End] Lose DullahanSinking and +2 Sinking CountSinking on target (max 30)Sinking on killed target/2) Sinking on 2 random enemies (max 8)
5 +463 (+3)Clash: 6-21Damage: 10-54.25Atk Weight:Dullahan and has 15+ SP, use 'Lament, Mourn, and Despair' as Counter (once per turn)
[Combat Start] If this unit does not have Dullahan, gain 1 Dullahan next turn (once per turn)
[On Use] Coin Power +1 for every 3 Sinking on target (max 2)
[Clash Win] Gain 
Offense Level Up next turn equal to (# of Clashes/3) (max 3, once per turn)
[Turn End] If this unit has Dullahan, lose DullahanSinking and +1 Sinking CountDullahan, mount Dullahan.
- Lose 5 SP every time this unit mounts Dullahan
- If 3+ allies have been defeated in this Encounter, gain Dullahan next turn. (once per Encounter)
- If this unit gets Staggered due to damage or raised Stagger Threshold when mounting Dullahan, recover from Stagger. If the Stagger is something that cannot be naturally recovered from, this unit does not mount Dullahan.
- Gain 1 Coffin when killing the target.
x5Sinking on target (max 15%)
- When, during combat, 1 ally takes damage that would kill them, consume 2 Coffin to apply 
Wild Hunt to them (2 times per turn)
- Apply 2 Damage Up next turn to the ally that has Wild Hunt
- If the said ally is from Wuthering Heights or Edgar Family, apply 1 Attack Power Up next turn as well
x3Sinking Potency and Count using their Skill and Coin Effects of their Attack Skills (2 times per turn)