Necrobinder Build

💀 Osty's Warband

Name: 10 Easy Tips For Necrobinder Builds in Slay the Spire 2
Channel: Ic0n Gaming

Feed the skeleton, let the skeleton kill

Updated for Early Access patch 0.104.0· Updated 2026-06-06

AIntermediate

SummonOstyScalingMinion

Win condition: Stack Osty's Max HP with Summon effects so his HP-scaling attacks (Unleash, Protector, Squeeze) hit for absurd numbers, while Osty's body absorbs enemy attacks and Necro Mastery converts every point of HP he loses into damage on every enemy.

A-Tier
Tier: Intermediate
Difficulty: 12
Core cards: Strong all-rounder
Power

Reviewed by SpireForge Editorial

Updated 2026-06-06

Strategy informed by Baalorlord, Ic0n Gaming

Deck core

Core cards

The cards this build is built around — prioritize these on every run.

Must-pick

Flex picks

Synergy

Relic priorities

What to grab from shops, bosses and chests to power the engine.

Phylactery UnboundCore
Summon 5 at combat start plus 2 every turn — free Osty fattening every fight.
Bone FluteCore
2 Block every time Osty attacks; with Rattle/Squeeze chains this is a real defensive layer.
Bound PhylacteryStrong
The other starter: Summon 1 each turn keeps Osty topped up between bursts.
AnchorStrong
10 Block at combat start buys time during the slow Summon-up turns.
VajraSituational
Flat Strength touches your own (non-Osty) attacks; minor, take if nothing better.
MangoSituational
Max HP keeps you alive through the slow opening.

Game plan

How to play

Step-by-step through the run, from opening hands to the win.

Open by fattening Osty
Lead with your biggest Summon effects — Reanimate (Summon 20), Necro Mastery, Pull Aggro, Afterlife — before you start swinging. Osty's HP IS your damage and your wall, so the more you Summon before attacking, the harder Unleash and Protector hit and the more Necro Mastery can reflect.
Set up Necro Mastery first turn it's drawable
Necro Mastery is a Power: play it ASAP. After it's down, every chunk of HP Osty loses to enemy attacks is dealt to ALL enemies, so you actively WANT enemies to hit Osty. Pull Aggro and Sic 'Em keep their attention on him.
Chain Osty attacks within a turn
Order matters: play cheap Osty hits (Poke, Fetch, Right Hand Hand) before Squeeze and Rattle so those late attacks count the most prior swings. Flatten costs 0 once Osty has already attacked, so sequence it after a Poke.
Use Unleash and Protector as finishers
Unleash deals 6 + Osty's current HP; Protector deals 10 + Osty's Max HP and upgrades to 0-cost. Save these for the turn Osty is at full, fattened HP for the biggest single hit.
Block with the skeleton, not your face
Bone Flute gives 2 Block every time Osty attacks, and Pull Aggro / Spur add Block and healing while Summoning. If a fight is going badly, Sacrifice or Bone Shards convert Osty's whole body into Block (double his Max HP on Sacrifice), then rebuild.
Reset and re-summon
After cashing Osty in with Sacrifice or Bone Shards, immediately Summon again next turn (Invoke, Spur, Afterlife, the Phylactery's start-of-turn Summons). Osty respawns and scaling resumes.

Honest take

Pros & cons

Strengths

Damage and defense come from the same resource (Osty's HP), so building wide is efficient.
Scales hard into long elite/boss fights and handles big single targets well.
Bone Flute and Spur give a steady defensive floor without dedicating many card slots.

Weaknesses

Slow to come online — early turns are spent Summoning, not killing.
If Osty dies with no re-summon available you lose both your wall and your damage at once.
Multi-enemy waves can split focus and burst Osty before Necro Mastery pays off.

Opening

Mulligan & priorities

What to keep, what to ditch in your opening hands.

Keep any Power, especially Necro Mastery and Calcify — they define the turn-one curve.
Keep a big Summon (Reanimate, Pull Aggro, Afterlife) to start fattening Osty immediately.
Keep a cheap Osty attack (Poke, Fetch) to bank early swings for Squeeze/Rattle later.
Toss raw 'you deal damage' cards like Strike — this deck wants Osty doing the hitting.
Hold Sacrifice only if you're already low; otherwise you want Osty alive and growing.

Map strategy

Pathing

How to route the map to assemble the build and stay healthy.

Prioritize Summon density

Pick up multiple Summon sources so Osty is large by turn 2-3. Reanimate is the single best Max-HP spike in the pool; Pull Aggro and Spur double as defense. Don't dilute the deck with non-Osty payoffs.

Hunt the Osty relics

Bone Flute (Block per Osty attack), Calcify (Osty attacks +4/+6), and the unbound Phylactery starter compound directly. Take elites you can handle for relic chances, since this build is relic-hungry for the small Osty buffs.

Avoid these

Common mistakes

Swinging with Unleash/Protector before you've Summoned this turn — you waste their HP scaling.
Sacrificing Osty for value when no follow-up Summon is in hand, leaving you with no minion and no plan.
Playing Squeeze or Rattle first in the turn, before any other Osty attacks have been logged.
Skipping Necro Mastery as 'just a Summon' — its HP-loss reflection is the build's real damage source.
Letting enemies ignore Osty (no taunt) so his HP never converts to Necro Mastery damage.

Quick answers

FAQ

Common questions about the Osty's Warband Necrobinder build.

Why does Necro Mastery matter so much if it 'only' Summons 5?

The Summon is just the opener. Its real value is the second clause: whenever Osty loses HP, ALL enemies lose that much HP too. Once it's down, every hit the enemy throws at your fattened Osty becomes AoE damage back at the whole room, which is why you want enemies attacking Osty rather than you.

Should I play Unleash or Protector first?

Whichever sees the bigger HP number. Unleash adds Osty's current HP, so it drops if Osty has already been hit this fight; Protector adds Osty's Max HP and ignores current damage, and it becomes 0-cost upgraded. Fatten Osty with Summons first, then fire these on a turn his HP is high.

Is Sacrifice worth running if it kills my own minion?

Yes, as an emergency button. Sacrifice gives Block equal to double Osty's Max HP, so an over-fed Osty converts into a huge defensive wall. Only play it when you have a follow-up Summon (Invoke, Spur, Afterlife, or the Phylactery's start-of-turn Summons) queued to rebuild him next turn.

How do I get the most out of Squeeze and Rattle?

Both reward prior Osty attacks made the same turn — Squeeze gains +5/+6 per other Osty Attack and Rattle hits an extra time per prior Osty attack. Lead with cheap Osty pokes (Poke, Fetch, Right Hand Hand) and play Squeeze and Rattle last so they count the maximum number of swings.

Provenance

Sources & video guides

This build's strategy is informed by these community creators.

10 Easy Tips For Necrobinder Builds in Slay the Spire 2
Ic0n Gaming·20K·21:20