ネクロバインダー

• Type: Skill
• Cost: 1
• Effect: Retain. If Osty is alive, kill Osty and gain Block equal to twice Osty's Max HP.

A cost-1 Retain Skill that sacrifices Osty to gain Block equal to 2x Osty's max HP. If Osty has 25 max HP, that's 50 Block. At 15 max HP it's still 30 Block — a cost-1 Block rate you simply cannot get elsewhere.

Revive (Revive 25 full-heal) right before Sacrifice lets you spike Osty to 25 max HP and cash in for 50 Block at cost 1. Unlike Bone Shard (sacrifice Osty for 9 AoE + 9 Block), Sacrifice is purely defensive. If Necromastery (Osty HP loss -> AoE damage) is already installed, Sacrifice's Osty-kill also converts the HP loss into all-enemy damage, giving you 50 Block and ~25 AoE damage in one card. Retain lets you time the play perfectly.

Rating: A-tier — high-return Block spike; the Revive + Necromastery combo is the strongest play.

• Revive Osty to 25 HP, then Sacrifice for 50 Block
• With Necromastery installed, Sacrifice deals AoE damage on top of the huge Block
• Retain for precise timing — play it right before a big incoming hit
• After Sacrifice, re-Revive Osty quickly with Encouragement / Bodyguard / Bone Army

• Revive: Revive 25 max HP. Sacrifice immediately cashes that in for 50 Block
• Necromastery: Osty HP loss = AoE damage. Sacrifice's kill also AoEs the room
• Bodyguard: cost 0, Revive 5-7. Rebuild Osty fast after sacrificing
• Encouragement: Retain Revive 3 + Osty +5 HP. Re-Revive after Sacrifice
• Bone Shard: sacrifice Osty for 9 AoE + 9 Block. Pick Sacrifice or Bone Shard based on the turn's needs

• Necrobinder Necromastery Combo (Key card) (A-tier)