Boss Guide
Introduction
Boss fights are the defining moments of every Slay the Spire run. Act 1–3 each pull one boss at random from a pool of three, while Act 4 always ends with the Corrupt Heart. Winning is necessary but not sufficient — the HP you preserve carries directly into the next Act.
This guide covers all ten bosses, their action patterns, the critical mechanics you must understand before the fight begins, and the cards and Relics that change each matchup.
Pre-Boss Checklist
Build the habit of reviewing these items before every boss fight.
| Checkpoint | Recommended Action |
|---|---|
| HP level | HP ≤ 20, or 20+ damage taken in the last two fights: Rest instead of Smithing |
| Campfire use | Above 60% HP: Smith (upgrade). Below that: Rest |
| Boss Relic knowledge | Know the three relic options ahead of time and weigh their tradeoffs |
| Potion reserve | Keep at least one combat-relevant potion (attack, block, or healing) |
Match the Boss Relic to your current deck rather than to abstract power rankings.
Act 1 Bosses
Act 1 randomly selects one of Slime Boss, The Guardian, or Hexaghost.
Slime Boss — HP: 140
The simplest pattern of the three Act 1 bosses. The fight hinges on managing the Split correctly.
Action Pattern
| Turn | Action | Details |
|---|---|---|
| 1 | Goop Spray | Adds 3 Slimed cards to discard pile |
| 2 | Preparing | No action (charging) |
| 3 | Slam | 35 damage |
| Loop | Repeat | Cycles 1 → 2 → 3 indefinitely |
| HP ≤ 50% | Split | Splits into 2 large Slimes, each inheriting current HP |
Strategy
The key insight is that you can force Split before Slam fires. Deal 70+ damage by the end of Turn 2 and the boss Splits without the 35-damage hit. After Split, the two Slimes inherit whatever HP the boss had, so use AoE (Whirlwind, Cleave, Twin Strike) to clean both up at once.
Slimed cards are 0-cost dead cards, but if you hold Evolve or Fire Breathing, they become free draw or damage triggers — Slime Boss can actually fuel those builds.
| Preparation | Examples |
|---|---|
| AoE for post-Split clean-up | Whirlwind, Cleave, Twin Strike |
| Block for Slam (35 damage) | Pre-stack at least 35 Block on Turn 3 |
| Slimed synergy | Evolve, Fire Breathing |
The Guardian — HP: 240
The highest HP of the three Act 1 bosses, with a two-phase structure where Sharp Hide punishes attacking at the wrong time.
Phase 1 Action Pattern (Attack Mode)
| Order | Action | Details |
|---|---|---|
| 1 | Charging Up | Gains 9 Block |
| 2 | Fierce Bash | 32 damage |
| 3 | Vent Steam | Apply Weak 2 + Vulnerable 2 |
| 4 | Whirlwind | 5 damage × 4 hits |
| Trigger | Mode Shift | After taking 30 cumulative damage → shifts to Phase 2 |
Phase 2 (Defensive Mode)
Sharp Hide reflects 3 damage to the player for every Attack card played.
| Phase 2 Action | Details |
|---|---|
| Twin Slam | 8 damage × 2 hits |
| Defensive cycle | Primarily Block-based actions |
| Mode Shift back | After taking another 30 damage → returns to Phase 1 |
Strategy
The core strategy is "attack hard in Phase 1, switch to Skills and Powers in Phase 2." The Vent Steam → Fierce Bash sequence (Weak and Vulnerable before a 32-hit) is the most dangerous window — pre-stack Block before that turn.
In Phase 2, minimize Attack cards to avoid Sharp Hide reflections. Use Skill and Power cards, then concentrate all your Attack cards back in Phase 1 when it returns.
| Preparation | Examples |
|---|---|
| Skill/Power toolkit for Phase 2 | Avoid playing Attacks while Sharp Hide is active |
| High single-hit attacks | Concentrate burst damage into Phase 1 windows |
| Block for Fierce Bash (32 damage) | Pre-stack before the expected hit turn |
Hexaghost — HP: 250
The most mechanically unusual Act 1 boss. A 9-turn cycle and a Divider hit scaled off your max HP reward prior knowledge.
Action Pattern (9-Turn Cycle)
| Turn | Action | Details |
|---|---|---|
| 1 | Inferno (first combat only) | 2 × 6 damage + adds 3 Burn cards |
| 2 | Divider | floor(Max HP ÷ 12) × 6 damage |
| 3–8 | Searing Blow | Scaling fire hits |
| 9 | Inferno | 24 damage + adds 3 Burn cards + upgrades all Burn cards (2 damage per turn each) → new cycle begins |
Strategy
Two essential knowledge points define this fight.
Point 1: Divider scales off your max HP, not current HP. Ironclad at 80 max HP takes 80 ÷ 12 = 6 → 6 × 6 = 36 damage from Divider. Max HP 23 or lower caps it at 1 × 6 = 6 damage. While intentionally lowering max HP before the fight is an advanced tech, simply understanding the formula helps you budget Block for Turn 2.
Point 2: Inferno must be outpaced. Every 9-turn Inferno stacks more Burn cards and upgrades them all to deal 2 damage per turn. A deck that cannot kill Hexaghost within 9 turns faces compounding passive damage that eventually overwhelms any healing. Target roughly 28+ damage per turn.
| Preparation | Examples |
|---|---|
| Consistent damage output | Deck capable of 25–30 damage per turn reliably |
| Burn mitigation | Exhaust-based cards, Discard effects |
| Block for Divider | Up to 42 damage at 84 max HP |
Act 2 Bosses
Act 2 randomly selects one of Bronze Automaton, The Collector, or The Champ.
Bronze Automaton — HP: 300
Two minions that can steal your best card, plus a telegraphed Hyper Beam every 6 turns.
Action Pattern (6-Turn Cycle)
| Turn | Action | Details |
|---|---|---|
| 1–2 | Flail | 7 damage × 2 hits |
| 3–4 | Boost | Strength +3, Block +9 |
| 5 | Hyper Beam | 45 damage (stunned next turn) |
| 6 | Stun | No action |
| Repeat | Strength cumulative | +6 Strength per full cycle |
Bronze Orbs (2 minions, HP 52–58 each)
| Action | Details |
|---|---|
| Stasis (75%) | Absorbs the highest-rarity card from your deck; returns it on death |
| Attack | 7 damage |
Strategy
Kill the Bronze Orbs early. Stasis removes your best card from play until the Orb dies, which can cripple a run that depends on a key Rare or Uncommon. Use AoE to damage both the boss and the Orbs simultaneously.
Hyper Beam (Turn 5) gains the boss's accumulated Strength by cycle 2+, potentially hitting 55–65+. Pre-stack Block on Turn 4. Letting the fight drag causes Strength to scale out of control.
| Preparation | Examples |
|---|---|
| AoE damage | Clear Orbs while damaging the boss |
| 45+ Block for Hyper Beam | Begin stacking on Turn 4 |
| High burst to end quickly | Prevent runaway Strength accumulation |
The Collector — HP: 282
Instant minion deployment and a guaranteed Turn 4 Mega Debuff define the fight's early urgency.
Action Pattern
| Timing | Action | Details |
|---|---|---|
| Opening (confirmed) | Torch Head × 2 | Immediately summons 2 minions (HP 38–40 each) |
| Turn 4 (confirmed) | Mega Debuff | Apply Weak 3 + Vulnerable 3 + Frail 3 |
| Post-Turn 4 (alternating) | Buff | All enemies Strength +3, self Block +15 |
| Other turns | Attack | ~18 damage |
Strategy
The Mega Debuff on Turn 4 simultaneously reduces your damage output, increases damage taken, and reduces your Block gain — a triple penalty. Artifact-generating Relics or cards that counter status effects are high value here. Budget your defensive resources around Turn 4.
Torch Heads alive during Buff turns also receive Strength +3. Clearing them quickly with AoE keeps the Buff's impact minimal. Leaving one Torch Head alive while focusing the boss is a viable tactic to delay Buff rotations, but only if your AoE is limited.
| Preparation | Examples |
|---|---|
| Debuff counter | Artifact Relic, Clarity, Panacea |
| AoE for Torch Heads | Clear both within 2–3 turns |
| Stable Block source | Maintain Block generation after Mega Debuff |
The Champ — HP: 420
The highest HP among Act 2 bosses. The hidden trap is that every debuff you stack is wiped on Phase 2 entry.
Phase 1 Action Pattern
| Action | Details |
|---|---|
| Heavy Slash | 16 damage |
| Face Slap | 12 damage + Weak 2 + Frail 2 |
| Defensive Stance | Block +15 + Metallicize +5 (Block gained per turn end) |
| Taunt | Self Strength +2 |
| Gloat (every 4 turns, confirmed) | Apply Weak 2 + Vulnerable 2 to player |
Phase 2 (HP ≤ 50%: Anger Triggers)
| Transition Event | Details |
|---|---|
| Anger | Removes all debuffs from self + Strength +6 |
| Execute | Primary repeating attack afterward — heavy two-hit pattern |
Strategy
The defining rule: all debuffs on The Champ are stripped when HP drops below 50%. Poison stacks, Vulnerable, Weak — gone. Strength jumps by 6 on top. Any strategy that relies purely on building debuffs must either kill before the threshold or generate enough raw damage after the reset.
Metallicize provides passive Block every turn end, making prolonged fights increasingly favorable for the boss. Push hard in Phase 1, accumulate damage, and be ready to close out Phase 2 before multiple Execute hits compound.
| Preparation | Examples |
|---|---|
| Raw burst damage | Enough damage output to handle Phase 2 after debuff reset |
| Sustained Block | Counter ongoing Metallicize passive regeneration |
| HP management | 420 HP is the highest of any Act 2 boss; budget potions |
Act 3 Bosses
Act 3 randomly selects one of Awakened One, Time Eater, or Donu and Deca.
Awakened One — HP: 300
A two-phase boss that punishes Power card spam in Phase 1 and invalidates debuff builds on Rebirth.
Phase 1 Action Pattern
| Action | Details |
|---|---|
| Curiosity | Gains Strength +1 (upgraded: +2) each time the player plays a Power card |
| Slash | 10 damage × 2 hits |
| Regenerate | Heals +10 HP at turn end |
| Dark Eye | 5 damage + adds status cards to player deck |
Phase 2 (After Rebirth)
| Transition Event | Details |
|---|---|
| Rebirth | After first kill: removes all debuffs + full HP restore → Phase 2 begins |
| Dark Echo | 40 damage (primary Phase 2 attack) |
Strategy
Curiosity's Strength stacking is the primary threat in Phase 1. Demon Form (Ironclad), Electrodynamics (Defect), and other multi-turn Powers continuously feed the counter. By mid-Phase 1, the Awakened One can be hitting for 30+ per attack if left unchecked. Minimize Power card plays or prepare to burst the boss before its Strength compounds.
The Regenerate (+10 HP per turn end) makes incremental damage strategies ineffective. High burst is generally safer than sustained DoT approaches.
Rebirth erases all debuffs and restores full HP — Poison stacks, Vulnerable, everything resets. Both phases require the same standalone burst capability.
| Preparation | Examples |
|---|---|
| Minimize Power card plays | Avoid feeding Curiosity in Phase 1 |
| Two-phase burst damage | Must maintain kill pressure through Rebirth |
| Counter Regeneration | Sustain 10+ damage per turn above HP regen |
Time Eater — HP: 456
The highest HP among Act 3 bosses. Time Warp — an automatic turn-end trigger at 12 cards played — dismantles Shiv builds and infinite loops entirely.
Action Pattern
| Action | Details |
|---|---|
| Ripple | 12 damage × 3 hits (36 total) |
| Head Slam | 26 damage + Draw reduced by 1 (until next combat) |
| Reverberate | Block +20 + applies debuffs |
| Time Warp | Playing the 12th card in a turn forces turn end + Time Eater Strength gain (permanent, cumulative) |
| Haste (HP ≤ 50%, once) | Removes all debuffs from self + recovers 50% HP |
Strategy
Time Warp is the defining constraint. Every card played beyond 11 in a single turn ends the turn immediately and permanently increases the boss's Strength. Shiv decks that typically play 15–20+ cards per turn are functionally broken here. Infinite combo builds (Watcher's Infinite, Defect loop) also collapse against this mechanic.
The correct adaptation is high-impact cards that deal significant damage per play. Whirlwind, Meteor Strike, Battle Trance, and high-cost power cards are ideal — they maximize damage-per-card-played within the 11-card window.
The Haste trigger at 50% HP erases all your debuffs and heals significantly. Avoid committing potions immediately before this threshold. After Haste fires, shift back to raw damage without debuff dependency.
| Preparation | Examples |
|---|---|
| High damage-per-card | Whirlwind, Meteor Strike, Bash, Immolate |
| Avoid Shiv/infinite builds | These approaches are entirely suppressed by Time Warp |
| Post-Haste damage | Maintain non-debuff-dependent damage through the second half |
Donu and Deca — HP: 250 each, Artifact × 2 each
A dual-boss fight where Donu's Ring of Fire and the four combined Artifact stacks create compounding threats.
Donu's Action Pattern
| Action | Details |
|---|---|
| Ring of Fire | Applies Strength −3 to player (permanent, cumulative) |
| Attack | ~10 damage |
| Pattern | Ring of Fire → Attack → alternating |
Deca's Action Pattern
| Action | Details |
|---|---|
| Beam | ~12 damage beam attack |
| Square of Protection | Grants Block +16 to both Donu and Deca |
| Pattern | Beam → Square of Protection → alternating |
Strategy
Kill Donu first. Ring of Fire debuffs the player's Strength every two turns — cumulative and permanent for the fight. After three or four cycles you are dealing significantly less damage on every attack. Deca's Square of Protection (Block +16 to both) is annoying but manageable if Donu is removed early.
All four Artifact stacks (2 per boss) mean debuffs require multiple applications to stick. Debuff-reliant builds must exhaust the Artifact stacks before the debuffs land. AoE that simultaneously hits both bosses efficiently strips Artifacts while building damage.
Square of Protection makes passive or low-DPS builds progressively worse — if you are not continuously outputting high damage, the block regenerates faster than your offense.
| Preparation | Examples |
|---|---|
| High AoE damage | Strip Artifacts while dealing spread damage |
| Kill Donu first | Prevent compounding Strength reduction |
| Consistent high DPS | Outpace Square of Protection's block regeneration |
Act 4 Boss
Corrupt Heart — HP: 750
Act 4's boss requires collecting three Keys first and can only be reached by completing Act 3 with Ironclad, Silent, or Defect (Watcher unlocked separately).
Reaching Act 4: Three Keys Required
| Key | How to Obtain |
|---|---|
| Ruby Key | Choose "Recall" at a Campfire (instead of Rest or Smith) |
| Emerald Key | Defeat the special Elite marked with a flame icon |
| Sapphire Key | Choose the Key instead of a Relic at any non-Boss chest |
Passive Abilities
| Ability | Details |
|---|---|
| Beat of Death | Player takes 1 damage per card played (Ascension 19+: 2 damage) |
| Invincible | Maximum 300 damage receivable per turn; requires a minimum of 3 turns |
Action Pattern
| Turn | Action | Details |
|---|---|---|
| 1 (confirmed) | Debilitate | Apply Weak 2 + Vulnerable 2 + Frail 2 + add 5 status cards to deck |
| 4 (confirmed) | Buff | Strength +2 (1st time) |
| 7 (confirmed) | Buff | Strength +10 (2nd time) |
| 10 (confirmed) | Buff | Strength +50 (3rd time — each Blood Shots hit exceeds 100+ damage) |
| Other | Blood Shots | 2 damage × 12 hits (Strength-dependent) |
| Other | Echo | 40 damage (fully blocked by Buffer / Intangible) |
Strategy
The Corrupt Heart fight is fundamentally about minimizing cards played per turn while maximizing damage output. Beat of Death taxes every card play by 1 HP, so decks that play 10–15 cards per turn sustain enormous self-damage before the boss even acts.
Tungsten Rod (Relic: take 1 less damage from all sources) is the strongest single counter — it reduces Beat of Death damage to zero, entirely eliminating the mechanic. If you have it, the fight transforms dramatically.
Turn 4 → 7 → 10 Strength buffs (+2 → +10 → +50) are the clock of the fight. After Turn 10, Blood Shots become a 24+ × 12-hit barrage that kills most builds in a single turn. Realistically, very few decks can kill 750 HP in 9 turns (requires ~84 damage per turn). The practical goal is ending the fight by Turn 12–14, or having the Block and HP to survive the Strength spikes.
Weak is exceptionally effective here — Blood Shots' 12 hits each benefit from Weak's 25% reduction, compounding the damage mitigation substantially. Buffer and Intangible counter Echo (40 damage) completely.
Poison builds (Silent) work well because layering Poison stacks requires few card plays, letting you deal massive damage with minimal Beat of Death self-damage.
| Preparation | Details |
|---|---|
| Tungsten Rod (Relic) | Negates Beat of Death entirely — highest priority if available |
| Low-card-count high-damage cards | Whirlwind, Meteor Strike, Poison stacking |
| Buffer / Intangible | Completely negates Echo (40 damage) |
| Weak application | Reduces all 12 Blood Shots hits by 25% |
| Poison build (Silent) | Deals damage through passive stacks with minimal card plays |
Boss Difficulty Summary
| Act | Boss | HP | Primary Threat | Difficulty |
|---|---|---|---|---|
| 1 | Slime Boss | 140 | Slam 35 + Split management | ★☆☆☆ |
| 1 | The Guardian | 240 | Sharp Hide + Fierce Bash 32 | ★★★☆ |
| 1 | Hexaghost | 250 | Divider scaling + Burn accumulation | ★★★☆ |
| 2 | Bronze Automaton | 300 | Hyper Beam 45 + card theft | ★★☆☆ |
| 2 | The Collector | 282 | Turn 4 Mega Debuff | ★★★☆ |
| 2 | The Champ | 420 | Debuff wipe + Metallicize | ★★★★ |
| 3 | Awakened One | 300 | Rebirth + Curiosity stacking | ★★★☆ |
| 3 | Time Eater | 456 | Time Warp + Haste | ★★★★ |
| 3 | Donu and Deca | 250 each | Strength stacking + Artifact ×4 | ★★★☆ |
| 4 | Corrupt Heart | 750 | Beat of Death + Strength +50 | ★★★★★ |
This article covers the original Slay the Spire (STS1). Some values vary by Ascension level.