Necrobinder: keep Osty useful and time Doom

Summoning a living Osty increases both current and combat maximum HP. Summoning while he is dead revives him with the Summon amount. Unleash reads current HP; Sacrifice reads maximum HP. Ordinary Osty attacks need him alive.

Kingy example: an intended 14 damage meets 5 Block and Osty at 6 HP. The remaining attack is 9: Osty takes 6 and Necrobinder takes 3. This example excludes other modifiers and direct HP loss.

Doom executes when the affected unit ends its turn at HP no greater than its Doom. Artifact can cancel an entire application. End of Days is an immediate-check exception.

If an enemy has 20 HP and 20 Doom, ordinary Doom has met the threshold, but you still need to survive its pending action. An additional ordinary Doom card may accomplish less than Block on that turn.