Slay the Spire 2 Final Boss Guide
Slay the Spire 2 has multiple boss encounters across its acts. This guide covers Soul Fysh (the Underdocks Act 1 boss), the Act 3 final bosses, and answers the big question returning players always ask: is the Heart in the game?
Is the Heart in Slay the Spire 2?
No — the Corrupt Heart is not in Slay the Spire 2. Runs currently end after defeating the Act 3 boss. There is no Act 4 or hidden final boss in the current Early Access build. The developers haven't confirmed whether it will be added later.
Soul Fysh — Underdocks Boss
Soul Fysh is the final boss of the Underdocks, an alternate Act 1 area. It's not the game's final boss, but it's one of the trickiest encounters in Act 1 due to its Beckon status card mechanic.
What is Beckon?
Beckon is a status card Soul Fysh places in your deck. It costs 1 Energy — if you fail to exhaust or discard it before your turn ends, it deals 6 unblockable damage. No amount of block preparation will save you. Soul Fysh places Beckons in both your draw pile and discard pile, so they cycle through your hand unpredictably.
5-Turn Attack Pattern
Soul Fysh places one Beckon in your draw pile and one in your discard pile. It doesn't attack. Use available Energy to deal early damage — don't panic about the Beckons yet.
Soul Fysh attacks for over 15 damage. If you haven't drawn Beckons, block and pour damage into the boss. This is your primary offensive window. Discard any Beckons you've drawn.
Incoming attack drops below 10 damage, but Soul Fysh adds another status card to your draw pile. Since the hit is light, prioritize offense here.
Soul Fysh buffs itself with Intangible — all damage you deal is reduced to 1. Unload everything BEFORE the buff resolves. Prepare blocks for the next turn.
Soul Fysh stays Intangible and inflicts 3 stacks of Vulnerable while dealing 10+ damage. Shift fully into defense — block the hit and exhaust any Beckons in hand.
Second Rotation Warning
After the first 5-turn cycle, the 3 Vulnerable from Turn 5 kicks in — you now take 50% more damage from all attacks. Tanking hits is no longer viable. Shift to block-first thinking and hunt for the finishing blow. If Soul Fysh is still above 50% HP entering rotation two, the fight becomes significantly harder.
Best Cards Against Soul Fysh
Exhaust beats discard — exhausted cards are permanently removed from the fight, not just cycled back in.
Act 3 — The True Final Boss
The Act 3 boss is the final encounter of a standard run. There are multiple possible Act 3 bosses — you can see which one you're facing by checking the map before the fight.
Ascension 10: You fight two Act 3 bosses simultaneously. Your deck needs sustained output across two full health bars — burst-only strategies fail here.
Frequently Asked Questions
What is the final boss of Slay the Spire 2?
In the current Early Access build, runs end after defeating the Act 3 boss. There are three possible Act 3 bosses. If you take the alternate Underdocks path in Act 1, you'll also face Soul Fysh as that act's final boss.
Is the Heart in Slay the Spire 2?
No. The Corrupt Heart from the original game does not appear in Slay the Spire 2. There is no Act 4 or hidden final boss in the current version. Runs end after the Act 3 boss.
Will the Heart be added later?
The developers haven't confirmed it, but given how central the Heart was to the original game, many players expect a similar final challenge to appear in a future update.
What is Soul Fysh?
Soul Fysh is the final boss of the Underdocks — an alternate Act 1 area. It's not the game's final boss, but it's a challenging mid-run encounter that uses the Beckon status card mechanic to deal unblockable damage.
What are the Act 3 bosses in Slay the Spire 2?
The Act 3 bosses include the Doormaker and others. At Ascension 10, you fight two Act 3 bosses simultaneously.
How do I deal with Beckon cards from Soul Fysh?
Beckon costs 1 Energy — if you don't exhaust or discard it before your turn ends, it deals 6 unblockable damage. Use cards like Acrobatics or Burning Pact to cycle them out. Exhaust is better than discard since exhausted cards are permanently removed.
Related guides