10 Boss Encounters and the Heart

Prepare from the map's boss icon

Acts 1–3 each have 3 possibilities. At A20, only Act 3 has 2 consecutive bosses. The main thresholds differ: HP at A9, attack damage at A4, and stronger special actions at A19. Do not combine them in one column.

• HP is shown as normal / A9 and above. For attack damage, prioritize the in-game intent including Strength, Vulnerable, and other modifiers.
• The Transient is a regular Act 3 enemy, not an elite. Taskmaster and Gremlin Leader are Act 2 elites.

Act 1: 3 bosses

• Example with normal Slime Boss at 140 HP: dropping it from 71 to 20 before splitting produces 2 large slimes with 20 HP each. This is easier than stopping at half HP, 70. Change plans if waiting means taking the heavy attack.
• Hexaghost's turn-two base damage per hit is floor(current HP / 12) + 1. At 24 HP, 3 × 6 = 18; at 36 HP, 4 × 6 = 24. Choose Rest or Smith while also considering survival later in the fight.

Act 2: 3 bosses

• The Champ's half-HP threshold is 210 normally, or 220 at A9+. Control damage and keep Vulnerable, Poison, and Strength reduction to use after the cleanse.
• Prepare to block the Automaton's heavy attack by turn six. Displayed damage changes with Ascension and enemy Strength; do not plan defense from a fixed base value alone.

Act 3: 3 bosses

• Defeating the Awakened One's first form does not end combat. While it awaits revival, targeted attacks are unavailable; on revival it cleanses debuffs. Do not assume Blasphemy is safe merely because it kills form one.
• Curiosity grants 1 Strength per Power normally, or 2 at A19+. In form two, play needed Powers without Curiosity's Strength penalty.
• At a Time Eater counter of 10, only 2 cards remain before forced turn end. Playing 2 zero-cost attacks first leaves no room for defense. Block or exit your stance before the 12th play.

Act 4: Spear and Shield, then the Heart

The fixed order is Rest Site → shop → Spear and Shield → Heart. Spear and Shield are an elite encounter, not a boss.

1. Do not spend the opening hand only on setup: prepare defense for the Spear's multi-hit turn two. At A18+, 2 Burns crowd the next hand.
2. Read the current intents and choose your last targeted action so you face the stronger attacker. Do not assume area attacks let you freely choose facing.
3. Kill one first to end Surrounded and reduce combined attacks. Use your hand to decide between finishing the lower-HP Shield and removing the Spear's Burns and multi-hits.
4. There is no Rest Site or shop afterward. Save HP and potions for the Heart, but do not lose here by hoarding them.

Handle the Heart's defenses and attacks separately

It is not immune to Poison. Treat Beat of Death, Artifact, and the per-turn HP-loss cap as separate mechanics.

1. Set up long-fight effects on turn one. Setup cards and Miracles also trigger Beat of Death, so check current HP and Block placed beforehand.
2. On turns two and three, read intents to see whether the single or multi-hit attack comes first. Match Piercing Wail to multi-hits; account for Buffer charges when using it against a single hit.
3. Buffs reset negative Strength, so avoid temporary Strength reduction on a buff turn. Once Artifact is added, reassess how debuffs will land.
4. Silent can use Poison. However, Artifact can stop the applying card's debuff, and Invincible can leave HP remaining. Keep a hand capable of defending again.
5. Prepare defense during card play, such as evoking Frost as Defect or using an exit card as Watcher. Check it separately from end-of-turn-only defense.

• Listed attack values precede Strength, Weak, Vulnerable, stance, and other modifiers. Calculate using the enemy's displayed damage and current status.

The Guardian: force a mode change before the heavy attack

It begins by charging. Defensive Mode triggers from damage that reaches HP, so do not subtract damage absorbed by its Block directly from the remaining Mode Shift counter.

1. Read the intent and remaining Mode Shift. It is not the same number as the boss's HP; check the displayed power counter first.
2. To stop a heavy attack, estimate damage spent on Block separately from damage reaching HP. Once it is insufficient, return remaining energy to defense or use potions.
3. Meeting the condition changes the current intent to defense and grants the boss 20 Block. Do not continue assuming all remaining attacks reach HP.
4. During defense, also count the card plays that trigger retaliation. Distinguish setup with Skills or Powers from chaining Attacks.
5. On returning to offense, read the new Mode Shift value. Do not repeatedly plan to interrupt using the first transition's requirement.

• The normal cycle is Charging Up → Fierce Bash → Vent Steam → Whirlwind. After a defensive phase it returns through Whirlwind, so do not treat the whole fight as a fixed four-turn loop.

Count the Guardian's transition thresholds and retaliation

• Each next requirement rises by 10. Do not confuse the current remaining counter with the next initial threshold. This table uses normal difficulty; Ascension breakpoints and retaliation values are outside this supplement's confirmed table.
• With no Block and 12 Mode Shift remaining, at least 12 damage reaching HP triggers the transition. Whether you can kill the boss is a separate calculation from remaining HP.
• At 3 retaliation, playing 2 Attack cards causes 6 total retaliation. A single multi-hit Attack counts as 1 card play and causes 3. This table excludes other damage and defensive effects.

Slime Boss: trigger Split, then deal more damage in the same turn

Its opening sequence adds Slimed, prepares, then makes a heavy single attack. Meeting the Split threshold changes the planned attack to Split, but does not require ending your turn immediately.

1. At the normal 140 HP, Split triggers at 70 or less. Read half of maximum HP separately from current HP inherited after splitting. Do not mix Ascension HP changes into this normal-difficulty example.
2. Even after the intent becomes Split, you can use remaining attacks or damage potions. Extra damage in the same turn lowers the HP of each upcoming large slime.
3. Killing it at 0 HP prevents the Split. If any HP remains, keep tools and defense to handle the resulting pair.
4. After splitting, reread both HP totals and next intents. Interrupting the original attack does not mean you have already prepared defense for the new large slimes.
5. Reducing a large slime to half HP splits it again into medium slimes. If you can kill one, compare that option with an area attack that may increase the enemy count.

The 2 large slimes inherit remaining HP at the moment of Split

Assumes 140 maximum boss HP, extra damage during the same player turn, and no other damage effects. Its remaining HP is not divided in half.

• An extra 20 damage reduces combined HP by 40 because each large slime inherits current HP. It does not permanently double the damage multiplier of extra attacks.
• These numbers are normal-difficulty examples only. Higher-Ascension HP and Split thresholds have not been added.

Hexaghost: turn-two thresholds and the later cycle

It first activates, then uses Divider. Afterward comes a seven-action cycle of Burns, double hits, and a buff. HP below is an assumed input for the current-HP calculation. Do not fix the reading time to entering combat or immediately before the hit; use actual intent to plan defense.

1. Take the referenced current HP as input, divide by 12, round down, and add 1. Finally multiply by 6 hits. Do not replace this input with maximum HP.
2. An input of 47 gives 4 × 6 = 24; 48 gives 5 × 6 = 30. Do not use this as a guarantee that healing or self-damage after intent is set will change displayed damage.
3. Do not deliberately lower HP beyond what you can survive later just to reduce the opening barrage. You still need HP for Burns, Tackle, and attacks after Inflame.
4. After surviving the opening 6 hits, count the cycle and actions until the next Inferno. It does not deal the same attack value every turn.

• The Divider table lists base values without Strength, Weak, Vulnerable, or defensive effects. The precise moment it reads current HP was not established across two source families, so remains unresolved. This does not guarantee that mid-turn healing or self-damage changes its power. Check the on-screen intent.

Divider base totals by HP range

• The table stops at 107 HP to divide examples into 9 ranges, not because that is the game's maximum-HP cap. The same formula works above this.
• These are arithmetic comparisons of the opening attack on normal difficulty. This is not a fixed table incorporating all other Ascension-dependent attack values.

This supplement adds steps and calculations for Act 1's 3 bosses

Scope: normal rules of the original PC game. Sources including V2.2 adjustments and the official V2.3.4 announcement were checked. Current executables, ports, mods, Slay the Spire II, and the board game require separate checks.

• The existing list of all 10 boss encounters across Acts 1–4 is retained. Do not count this supplement as 7 new bosses or complete action tables for all 10.
• Damage dealt means damage reaching enemy HP; when counting the Guardian's retaliation, count Attack cards played, while hits count the times one Attack connects. Do not add transition requirements and retaliation using mismatched units.
• These calculations compare fixed inputs. Win rates including draw order, upgrades, relics, and potions, or a strongest sequence reproducible with every deck, have not been tested.
• Added cycles cover normal difficulty cross-checked against guides by independent authors. Complete Ascension-dependent HP, damage, and transition numbers, and shared editorial history between sources, are outside the newly confirmed tables.