Slay the Spire 2 Necrobinder Build Guide: Best Osty Summon Deck

If there’s one thing I didn’t expect from Slay the Spire 2, it’s how quickly the Necrobinder became my favorite—and most frustrating—character. On paper, 66 max HP feels like a joke. In practice, once you understand how to play around Osty, it turns into one of the most satisfying and strategic playstyles in the game.

This isn’t just another dry guide. This is the kind of build I keep coming back to after failed runs, thinking: “Okay, one more try—I know I can make this work.” And when it does? It feels borderline unfair.

Why the Osty Build Actually Works

At first glance, Osty seems like a gimmick. A big skeletal hand that tanks damage? Cool, but unreliable—right?

Not even close.

The real power comes from this simple idea:

Osty’s HP is basically permanent Block that doesn’t disappear.

That one mechanic changes everything. Instead of reacting to enemy damage every turn, you’re building a growing buffer that carries you through the entire fight.

Core Mechanics (Explained Like a Human Would)

1. Summon = Your Real Defense

Every time you play a Summon card: you increase Osty’s max HP, you restore him if he’s gone, and you effectively stack permanent survivability that carries between turns.

2. Osty Attacks = Your Real Damage

These attacks scale off Osty’s HP or usage, get stronger the longer the fight goes, and naturally convert your defensive scaling into offensive pressure.

3. Souls = Consistency Engine

You don’t need a full Soul build, but ignoring it is a mistake because even a small package helps you cycle faster, remove bad cards, and consistently find your key plays.

My Go-To Card Priorities

I’ve tested a lot of variations, and honestly, the Osty build feels best when you keep things simple and focused instead of overcomplicating your deck.

Early Game Must-Haves

Pull Aggro – This card carries Act 1 harder than it should
Snap – Retain is insanely underrated here
Blight Strike – Just solid early damage without setup

Mid-Game Power Picks

Rattle – One of the most satisfying scaling attacks in the build
High Five – AoE plus Vulnerable gives huge tempo advantage
Delay – Energy flexibility wins difficult turns
Spur – Reliable sustain for long fights

Late Game Win Conditions

Unleash – Your main boss-finisher
Squeeze – Turns every Osty hit into scaling damage
Necro Mastery – Converts defense into passive AoE pressure
Reanimate – Massive burst of Summon value when needed

Quick Tier Overview

Tier	Focus	Key Idea
Early	Survival	Build Osty as fast as possible
Mid	Scaling	Add multi-hit and AoE tools
Late	Execution	Convert HP into lethal damage

Relics That Actually Matter

Not all relics are equal here, and some feel like they were designed specifically to support this playstyle.

Bound Phylactery – Passive scaling every turn without effort
Bone Flute – Turns Summon cards into real defensive value
Book Repair Knife – Allows aggressive routing without punishment
Friendship – Extra energy is almost always worth the trade

If there’s one standout, Bone Flute makes your entire run feel stable and consistent.

How I Approach Each Act

Act 1 – Don’t Get Fancy

This is where most runs fall apart, so your priority is simple survival through reliable damage and early Summon scaling without overcommitting to slow setups.

The biggest mistake here is drafting complex power cards too early instead of stabilizing your deck.

Act 2 – The Build Starts to Click

This is where Osty becomes a real engine, and your focus should shift toward adding AoE, improving draw consistency, and identifying your primary win condition.

If your deck feels clunky at this stage, it usually means you diluted your core strategy.

Act 3 – Cut the Fat

By this point, your deck should feel clean and focused, so avoid unnecessary cards, remove weak options, and double down on what actually wins fights.

This is also where Unleash becomes devastating if Osty’s HP is properly scaled.

Slay the Spire 2 Best Decks: Meta Build Tier List (2026 Early Access Guide)

Common Mistakes I Made (So You Don’t Have To)

1. Thinking Osty Tanks Everything

If incoming damage exceeds Osty’s HP, the rest goes directly to you, which is extremely dangerous with such a low health pool.

2. Mixing Too Many Archetypes

Trying to combine Doom and Osty strategies leads to inconsistent draws and weak scaling, so it’s better to stay focused on one core plan.

3. Ignoring Card Draw

Without proper draw, you won’t find your Summon cards in time, which completely stalls your scaling and leads to lost runs.

Slay the Spire 2 Relics Spreadsheet: Guide to All Items, New Mechanics, and Beta Meta (2026)

What Makes This Build So Fun

The biggest appeal of this build is the sense of momentum, where you start fragile and vulnerable but gradually turn into an unstoppable force as Osty grows stronger.

At some point, fights shift from survival to full control, and enemies stop feeling threatening.