A Necrobinder keyword. Summon X increases Osty's max HP by X. If Osty is defeated, Summon also revives them.

Summon X is a Necrobinder keyword: the card increases Osty's max HP by X. If Osty is defeated, Summon revives them. Stacking Summon raises Osty's durability, which in turn absorbs more damage for the player.