Bound Phylactery

Bound Phylactery is the Necrobinder's starting relic in Slay the Spire 2, summoning 1 creature at the start of each turn. This persistent summoning effect ensures Osty, the Necrobinder's skeletal companion, is always being reinforced, providing a steady stream of HP to absorb incoming damage and fuel Osty-based attacks.

The turn-by-turn Summon from Bound Phylactery is the engine that makes the Necrobinder's low starting HP viable. Each Summon 1 either revives Osty with 1 HP or adds 1 HP to a living Osty, creating a buffer that accumulates if not consumed by enemy attacks. Cards like Poke, Flatten, and Rattle command Osty to deal damage, while Sacrifice can convert Osty's accumulated HP into a massive Block burst. The relic ensures that even without drawing Summon cards, Osty always grows by at least 1 HP per turn.

Bound Phylactery is essential for all three Necrobinder archetypes. Osty/Summon builds layer additional Summon effects from cards like Invoke and Grave Warden on top of the relic's passive summoning. Doom builds rely on Osty tanking damage while Doom stacks accumulate on enemies through Blight Strike and Death March. Soul builds need Osty alive to absorb damage while the Necrobinder pays HP costs for powerful Soul cards. Against bosses like Kaiser Crab where fights drag on, the cumulative Summon from Bound Phylactery can build Osty to massive HP totals. The upgraded version, Phylactery Unbound, summons significantly more per turn and is one of the most impactful relic upgrades in the game.