Slay the Spire / Original game

Combat Calculations, Card Choices, and Fixing Failed Runs

Examples for deciding the next turn from enemy intents, energy, draw pile, Block, and potions. Identify missing roles rather than relying on fixed deck sizes or strongest-card rankings.

Scope: Original game, PC Steam App 646570; includes the V2.2 balance changes. The official announcement with a confirmed version number is V2.3.4 (2022-12-20). Checked: 2026-10-02. Ports, mods, II, and the board game are separate.

What to read at the start of a turn

Check every enemy's intent and HP. Decide first whether you can kill an attacker or must Block its damage.
Add up current energy and hand costs. Count X costs, changed costs, Calm exit energy, and potion resources separately.
Before placing Block, check whether enemy Artifact will prevent Weak. Against the Heart, also defend Beat of Death during card plays.
When drawing for an answer, check that the needed card is still in the draw pile. Seek targets the draw pile; Hologram targets discard.
Before ending the turn, check whether you remain in Wrath, hold cards that cause HP loss, and know the enemy's next action.

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4 calculations from the basic rules

Situation	Calculation	Conditions for the decision
Normal Strike + Vulnerable	6×1.5＝9	Requires Vulnerable to have actually landed. Subtract enemy Block separately.
Normal Strike + Weak	6×0.75＝4.5→4	Round down to an integer. Assumes no Vulnerable, Strength, stance, or other modifiers.
8 Block against a 20-damage Attack	HP damage: 20 - 8 = 12	Recheck the final result with Wrath, Vulnerable, Torii, or other effects.
Blade Dance at the 10-card hand limit	Generated cards with no hand space go to discard	If you plan to play the Shivs, reduce hand size first.

These examples use a single modifier. With several multipliers, do not collapse order and rounding into one mental calculation; also check in-game card and intent displays.

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Take the reward or skip?

Identify a missing role for the next enemy: fast single-target damage, multi-enemy damage, defense, long-fight scaling, or draw.
Check costs with the offered card added to your current hand. More expensive setup that cannot be played on turn one also needs resources or draw support.
When a role is already covered, compare the marginal value of another card. Skip a reward that does not help.
Removal reduces the deck by 1 card. Consider weak starters or manageable Curses when other cards already cover needed attack and defense.
Do not fix the final size at 20, 45, or another number. Exhaust, draw, generation, and Retain change how many cards cycle during combat.

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Deciding when to use potions and Rest Sites

Use a potion before taking a lethal attack in that combat. Merely holding it does not defend you.
Choose a type that solves the current problem: insufficient Block, the answer still in the draw pile, or insufficient energy. With Sozu, used potions cannot be replaced.
Rest normally heals 30% of maximum HP. Compare current HP with expected damage from the next enemies to judge whether healing keeps you alive.
For Smithing, check how changes help now: Eruption 2 → 1 cost, Corruption 3 → 2, Seek selecting 1 → 2 cards. Upgrades do not always raise damage.
On a Heart run, Recall is an alternative to Rest or Smith at that site. Take the Ruby Key before running out of Rest Sites.

Potion	Normal effect	Uses and cautions
Block Potion / ブロックポーション	12 Block	Add defense against the current attack. Block normally disappears at turn end; do not assume it lasts next turn.
Fire Potion / 火炎ポーション	20 damage to 1 target	Check whether it kills an attacker. Does not deal 20 to all enemies.
Explosive Potion / 爆発ポーション	10 damage to all enemies	Reduce several minions. Add up the intents of surviving enemies too.
Energy Potion / エナジーポーション	2 energy	Resources when you already hold cards to play. Does not also draw cards.
Swift Potion / 加速ポーション	Draw 3	Check whether an answer remains in the draw pile, room within the hand limit, and No Draw effects.
Weak Potion / 脱力ポーション	Apply 3 Weak to the target	Reduces every hit of a multi-hit attack. Does not land while the target has Artifact.
Fear Potion / 恐怖ポーション	Apply 3 Vulnerable to the target	Raises subsequent Attack damage. Does not multiply all Poison or orb damage by 1.5.
Ancient Potion / 古代のポーション	1 Artifact	Blocks the next debuff. For the Biased Cognition synergy, use it first to prevent the Focus-loss effect.

These are 8 examples without Sacred Bark doubling. Two index families list 42 types, but this page does not claim to explain all 42 effects.

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Use the cause of a loss to improve the next run

Where you lost	Facts to review	Role to prepare next time
Ran out of HP before the first elite	Turns spent in regular fights and whether the elite could be avoided	Immediate damage, Rest, potions, and a detour.
Overwhelmed by Act 2's multiple enemies	Damage needed to remove one enemy and their combined intents	Area damage, debuffs, and focused attacks.
Insufficient damage in a boss's later phase	Whether damage per turn increased after setup	Strength, Poison, Focus, or similar scaling, plus defense to protect it.
Lost without drawing the needed card	Draw versus discard location, the hand limit, and any No Draw	Draw, Seek, Retain, and play order.
Lost HP whenever playing cards against the Heart	Beat of Death at 1 or 2 and whether Block was gained during card play	Block placed first, Exhaust synergies, and Block effects that land on their target.

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Combat Calculations, Card Choices, and Fixing Failed Runs

What to read at the start of a turn

4 calculations from the basic rules

Take the reward or skip?

Deciding when to use potions and Rest Sites

Use the cause of a loss to improve the next run

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