Slay the Spire 2 Deck Building Guide: How to Build Decks That Win

1. The 5 Golden Rules of Deck Building

Before diving into character-specific strategies, internalize these universal principles. They apply at every Ascension level with every character:

2. Card Evaluation Framework

When you're offered a card reward, ask these four questions in order:

The 4-Question Card Test

1. Does this card help me beat the next elite/boss? — If yes, strongly consider it.
2. Does this card synergize with cards I already have? — If yes, and it's Act 2+, it's likely a take.
3. Does this card solve a weakness in my deck? — No AoE? Take that Whirlwind. No block? Take that Shrug It Off.
4. Is this card better than an average draw from my current deck? — If no, skip it. This is the most underrated question.

Card Quality by Act

What constitutes a "good card" changes dramatically as your run progresses:

• Act 1: Any attack that deals 10+ damage for 1 energy is a take. You need damage output to kill elites. Even "bad" cards like Perfected Strike can carry you through Act 1.
• Act 2: Cards must do at least 2 things. A card that only deals damage with no utility is now questionable. AoE, debuff application, and card draw become premium.
• Act 3: Cards must be exceptional. You should skip 60-70% of Act 3 card rewards unless they directly perfect your existing game plan.

3. Energy Curve & Card Balance

A well-constructed deck has a smooth energy curve. Here's what to aim for:

Target Card Distribution (30-Card Deck)

• 0-cost cards: 2–4 — Great for energy efficiency, but too many wastes card draw.
• 1-cost cards: 15–18 — Your bread and butter. Most of your deck should be 1-cost.
• 2-cost cards: 5–8 — Powerful effects that define your strategy. Don't take too many.
• 3-cost cards: 1–2 — Game-changers like Demon Form or Echo Form. Only take if you have 4+ energy.

Attack-to-Skill Ratio

Aim for roughly 40% Attacks / 40% Skills / 20% Powers by mid-Act 2. In Act 1, you want closer to 60% Attacks because elites demand damage output.

4. Character Archetypes & Synergy Guide

5. Optimal Deck Size & Card Removal

How Many Cards Should Your Deck Have?

The eternal question. Here's the nuanced answer:

• 20–25 cards: Ideal for most runs. You cycle through your deck every 4-5 turns, seeing key cards reliably.
• 25–35 cards: Common at A15+ when you're forced to take more cards. Still functional if you have strong card draw.
• 15–20 cards: Viable with high-cycling builds (Silent discard, Defect Hologram loops). Risky — one status effect can wreck you.
• 35+ cards: Only acceptable with Corruption + Dark Embrace or other mass-draw engines. Generally too inconsistent.

Card Removal Priority Order

1. Strikes — Always remove first. They're the weakest attack cards and dilute your draws.
2. Curses — Remove immediately unless you have exhaust synergy (Ironclad) or discard synergy (Silent).
3. Defends — Remove once you have better block options (Shrug It Off, Footwork, Glacier).
4. Early-game filler — That Perfected Strike you took in Act 1 to beat Gremlin Nob? Remove it in Act 3 if it no longer serves your build.

At minimum, remove 2–3 Strikes over the course of a run. Each removal makes your deck noticeably better.

6. How Deck Building Changes Per Act

Act 1: The Foundation

Goal: Survive and build a damage baseline.

• Take almost any attack card offered in the first 3-4 floors.
• Priority 1: Damage. Priority 2: More damage. Priority 3: Block (only if you have enough damage).
• Aim for 3-4 attack cards before your first elite.
• Upgrade your best attack at the first campfire.
• If you see a premium scaling card (Demon Form, Noxious Fumes, Defragment), take it — but only one.

Act 2: The Transition

Goal: Build scaling and AoE. Your deck needs to handle groups.

• Stop taking generic attacks. Only take attacks with additional value (AoE, debuff, card draw).
• Add 1-2 strong block cards (Shrug It Off, Leg Sweep, Glacier).
• Prioritize AoE damage — Act 2 has many multi-enemy fights.
• Identify your win condition and start building toward it.
• Remove at least one Strike at a shop.

Act 3: The Refinement

Goal: Polish your deck for the final boss.

• Be extremely selective. Skip most card rewards.
• Only take cards that directly improve your existing win condition.
• Remove remaining Strikes and any dead weight.
• Buy key relics/potions at shops instead of cards.
• Know which boss you're facing and adjust: Time Eater needs efficient turns, Awakened One punishes Power spam, Donu & Deca need AoE + single-target.

7. Common Deck Building Traps

These mistakes kill more runs than bad RNG ever will:

🪤 Trap 1: "This Card Is S-Tier, I Must Take It"

A card isn't good in a vacuum — it's good in context. Offering is one of the best cards in the game, but taking it on floor 2 when you have no damage forces you to spend HP you don't have to spare. Evaluate cards based on your current deck state, not a tier list.

🪤 Trap 2: Chasing Archetypes Too Early

Picking Catalyst on floor 3 because "I want to play poison Silent" is a trap. You have no poison cards yet. Take what helps you survive NOW, and let the archetype emerge naturally from your card pool.

🪤 Trap 3: Ignoring Energy Economy

Taking every 2-cost card you see because they're powerful creates a hand where you can only play one card per turn. Count your deck's average energy cost. If most cards cost 2, you need an energy relic or energy-generating cards.

🪤 Trap 4: Not Enough Card Draw

A deck without card draw is at the mercy of its shuffle order. You need at least 2-3 sources of card draw or deck manipulation to find your key cards consistently.

🪤 Trap 5: Taking Too Many Powers

Powers are permanent value, but they cost energy and a draw the turn you play them. Playing 3 Powers in one turn means you did nothing that turn except set up — and died because you didn't block. Limit to 3-5 Powers per deck, and only take them when you have the energy to support them.

8. Advanced Concepts for A15+

Infinite and Near-Infinite Combos

At high Ascension, certain card combinations can create infinite (or functionally infinite) loops:

• Ironclad: Dropkick ×2 (with all enemies Vulnerable) = infinite damage. Sundial relic + Pommel Strike + Shrug It Off = infinite block and draw.
• Silent: Calculated Gamble + Tactician + Reflex + enough draw = infinite energy and card cycling.
• Defect: Recycle + Hologram + Turbo + small deck = infinite energy. Coolheaded ×2 + enough Focus = infinite block.

Don't force infinites — they require very specific setups. But recognize when you're close to one and pivot accordingly.

The "Hallway Fight" Calibration Test

At A17+, use hallway fights as deck calibration checks:

• Taking 0-5 damage from a hallway fight = your deck is ahead of the curve.
• Taking 5-15 damage = your deck is on pace. Normal.
• Taking 15-25 damage = your deck has a weakness. Identify and fix it immediately.
• Taking 25+ damage or using a potion = your deck is behind. Path conservatively and prioritize upgrades/shops.

Boss-Relative Deck Building

At the start of each act, check which boss you'll face and build accordingly:

• Slime Boss (Act 1): Needs strong single-target burst to split it at high HP. AoE is good for the split slimes.
• Guardian (Act 1): Needs consistent block every turn. Can't burst through its shell form — play the long game.
• Hexaghost (Act 1): Attack scales with your HP. Don't heal before this fight. Needs scaling damage for the Inferno turns.
• Collector (Act 2): Needs AoE to clear minions. Debuff removal (Weak/Crippling Cloud) helps.
• Bronze Automaton (Act 2): Needs strong block every 6th turn (Hyper Beam). Kill before the second Hyper Beam.
• Champ (Act 2): Don't bring him below 50% until you're ready to burst. The Execute phase is deadly.

Ready for the ultimate challenge? Read our Ascension Guide to conquer A1 through A20.