Sacrifice

Sacrifice is a rare Necrobinder skill with Retain that kills Osty if alive, granting Block equal to double Osty's Max HP. This card converts your skeletal companion into a massive defensive shield, potentially generating 30, 40, or even 50+ Block in a single play when Osty has been buffed through repeated Summoning.

Sacrifice creates a dramatic tension with other Osty cards. You want Osty alive for Poke, Flatten, and Rattle damage, but sometimes trading Osty for survival is the correct play. Since Bound Phylactery resummons Osty each turn, you can Sacrifice on one turn and have Osty back the next. Invoke and Grave Warden accelerate the resummon process. Shared Fate and Protector increase Osty's Max HP, making future Sacrifices even larger.

Sacrifice is one of the Necrobinder's strongest defensive options, especially against burst-damage bosses like Vantom and The Insatiable. The Retain keyword means you can hold it across turns, waiting for the perfect moment when Osty's HP is highest. In Osty/Summon focused builds, Sacrifice is the emergency button that converts your investment in Osty into survival. Against Test Subject #C10, alternating between building Osty and Sacrificing creates a sustainable defense loop.