Slay the Spire 2 Necrobinder Builds: Osty, Doom, and Souls Explained

Necrobinder Is the Best Character Right Now

I’ll say it plainly: Necrobinder is S-tier in the current Early Access meta. The character has three interlocking systems — Osty, Doom, and Souls — and the best decks blend all three. Where other characters have archetypes you pick between, Necrobinder wants you to use everything at once.

Starting HP is 75. Starting relic is Osty’s Binding, which summons Osty — a giant reanimated hand with its own HP bar that fights alongside you. You’re never alone.

Balance patches will likely tune this character down. But right now, Necrobinder is the strongest pick for climbing.

Early Access warning: numbers and card effects may change with updates.

System 1: Osty — Your Undead Bodyguard

Osty is a summon with its own HP pool. It intercepts ALL attacks aimed at the Necrobinder. Every hit the enemy throws goes into Osty instead of you. Think of it as a renewable Block pool that exists on a separate entity.

If Osty dies, it regenerates at the start of your next turn. You lose one turn of protection, but it comes back. The key is keeping Osty’s HP high so it never drops.

Core Cards

• Raise Hand — Summon 8. Adds 8 HP to Osty. Your bread-and-butter sustain card. Take 2-3 copies early. Keeping Osty healthy is the entire defensive strategy.
• Bone Wall — Summon 14 and gain Block. Massive Osty healing plus personal Block. One of the best defensive cards in the Necrobinder pool. Prioritize this.
• Necrotic Surge — Summon equal to Osty’s missing HP. This is the card that turns a near-death Osty into a full-health monster in one play. If Osty has 40 max HP and is at 5, Necrotic Surge heals it for 35. The worse the situation, the better this card gets. Absolute must-take.
• Flesh Shield — Gives Block based on Osty’s current HP. When Osty is healthy, this generates huge Block numbers for you personally.

How Osty Works in Practice

Turn 1: Osty is already on the field (Osty’s Binding summons it automatically). Enemies attack Osty, not you. You play Summon cards to keep Osty alive.

When Osty dies: You take direct damage until your next turn, when Osty regenerates. This is the danger window. Good Necrobinder play means Osty never dies — or if it does, you have enough personal Block to survive one turn.

The Osty + Necrotic Surge combo is the signature play. Let Osty tank down to low HP, then Necrotic Surge refills it completely. You get maximum value from the “Summon = missing HP” effect. It looks reckless but it’s actually the mathematically optimal line.

Relic Synergies

• Relics that trigger effects when you play Skills work well since most Summon cards are Skills.
• Relics that give Block at the start of turn help cover the gap if Osty goes down.
• Osty’s Binding (starting relic) — guarantees Osty in every fight. The foundation of everything.

System 2: Doom — The Execute Button

Doom is a debuff you apply to enemies. When an enemy’s Doom count equals or exceeds their current HP, they die at the end of their next turn. Not “take damage.” Die. Bypasses Block, armor, damage reduction, everything.

This is the Necrobinder’s answer to high-HP enemies and bosses with defensive mechanics. You don’t need to punch through 200 Block. You need to get their HP low enough that Doom catches them.

Core Cards

• Hex — Applies Doom to an enemy. Your basic Doom source. Multiple copies are good because Doom stacks — each application pushes the threshold higher.
• Spreading Doom — Applies Doom to ALL enemies. The AoE version. In multi-enemy fights, this sets up a potential board wipe.
• Wither — Deals damage and applies Doom. Dual-purpose — chip their HP down while simultaneously raising the Doom threshold. Extremely efficient.
• Death Sentence — A large Doom application. Your premium single-target Doom card for boss fights.

How Doom Works in Practice

Say an enemy has 80 HP. You apply 15 Doom through various cards. Then you deal 65 damage through normal attacks, bringing them to 15 HP. Doom (15) is now >= current HP (15). At the end of their next turn, they die instantly.

The math is Doom + damage from two different angles. You’re not replacing your attack cards with Doom cards — you’re supplementing them. Hit the enemy normally while stacking Doom on the side. Eventually the two lines cross and the enemy just drops.

Where Doom Shines

• Bosses with damage reduction or huge Block — Doom ignores all of it. If Doom >= HP, they’re dead.
• Enemies that heal — Healing doesn’t remove Doom. They can heal all they want; if you push Doom past their HP threshold, it’s over.
• Multi-enemy fights (with Spreading Doom) — Apply Doom to everything, do some AoE chip damage, watch the room collapse.

Common Pitfall

Relying on Doom alone. Doom needs the enemy’s HP to actually drop below the threshold. If you load up on Doom cards but have no attacks, the enemy sits at 80 HP with 50 Doom forever. You need damage cards too. Doom is the closer, not the opener.

System 3: Souls — The Cycle Engine

Souls are zero-cost cards that draw 2 cards when played. That’s it. No damage, no block, just cycling. But that simplicity is exactly why they’re so good.

Playing a Soul costs nothing and replaces itself plus one extra card. Your turns get longer. You see more of your deck. You find Necrotic Surge when Osty is dying. You find Hex when the enemy is almost in Doom range. Souls are the glue that makes everything else consistent.

Core Cards

• Lost Soul — The baseline Soul card. Costs 0, draws 2. Take them.
• Wandering Soul — A Soul with a small bonus effect on top of the draw. Slightly better than Lost Soul.
• Soul Harvest — Generates or interacts with Souls in your deck. Helps ensure you always have Souls in hand to keep cycling.

How to Use Souls

Play them immediately. There’s almost never a reason to hold a Soul in hand. It costs 0, draws 2, and makes your turn better. The only exception is if you’re about to reshuffle your discard pile and you want specific cards back on top — but that’s rare.

In a well-built Necrobinder deck, you might play 2-3 Souls in a single turn, drawing 4-6 extra cards. That’s how you find your key plays every single turn instead of hoping they show up.

The Danger of Too Many Souls

This matters. If your deck is 40% Souls, you’re drawing Souls that draw into more Souls that draw into more Souls. You cycle your entire deck and find… nothing worth playing because you didn’t take enough real cards. Souls amplify your deck’s quality. If the quality isn’t there, amplifying nothing gives you nothing.

3-5 Souls in a deck is the sweet spot. Enough to smooth out your draws without flooding your hand.

Putting It All Together: Blended Builds

The best Necrobinder decks aren’t “Osty decks” or “Doom decks.” They’re all three systems working together.

The Standard Necrobinder Gameplan

Early turns: Osty tanks. You play Summon cards to keep it healthy and Souls to cycle through your deck.

Mid-fight: You start applying Doom to the main threat while using normal attacks to chip HP. Osty is still absorbing all incoming damage.

The kill turn: Enemy HP drops below their Doom threshold. They die at end of turn. You didn’t need to do the last 15-30 damage yourself — Doom handled it.

Sample Priority List for Card Picks

1. Bone Wall — Best defensive card. Summon + Block.
2. Necrotic Surge — Best Osty recovery. The “oh no” button that always saves you.
3. Hex / Wither — Doom application. You need 3-4 Doom sources to threaten bosses.
4. Raise Hand — Reliable Osty sustain.
5. Lost Soul (first 3-4 copies) — Cycle consistency.
6. Spreading Doom — AoE Doom for hallway fights.
7. Death Sentence — Big single-target Doom for bosses.

Boss Matchups

Necrobinder is strong against most bosses in the current patch. Osty absorbs predictable attack patterns while you stack Doom. Bosses that deal damage through effects that bypass Osty (AoE, debuffs) are harder — you’ll need personal Block cards for those.

Bosses with high HP pools and lots of armor or Block are actually easier for Necrobinder than for most characters. Doom doesn’t care about armor. It checks HP, and if Doom is higher, the boss dies.

General Necrobinder Tips

• Osty’s HP is your real health bar. Track it carefully. Let it dip low for Necrotic Surge value, but never let it die if you can avoid it.
• Doom is a supplementary win condition, not your only one. Build enough attack damage to get enemies into Doom range.
• Souls make your deck consistent, but they don’t make it good. Take real cards first, Souls second.
• Necrotic Surge is arguably the best card in the Necrobinder pool. Upgrade it early (higher Summon value means bigger heals for Osty).
• Keep your deck tight. With Souls providing card draw, a lean 25-card deck cycles incredibly fast. You’ll see every card almost every fight.
• Check our Card Tier List for current Necrobinder card rankings and our Elite Guide for which elites give Necrobinder trouble.