Combat Undo

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StS2 Undo lets you reverse a card play, a potion use, or an entire turn
during combat in Slay the Spire 2. Misclicked a card on the wrong target?
Played a Power before drawing? Burned a key potion at the wrong moment?
Press Z and the combat snaps back to the moment right before that
action — HP, block, energy, draw/discard order, monster intents, RNG,
animations, and all.

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On the STS2 beta branch?

This file (Sts2UndoMod-v0.0.12.zip) is the
stable-branch build. If you have opted into the STS2 beta in
Steam (right-click Slay the Spire 2 → Properties → Betas), grab the
beta-branch build instead — open the Files tab on this mod page
and download Sts2UndoMod-v0.0.12-beta.zip from
there. Running this stable dll on the beta branch (or vice versa)
throws MissingMethodException at the first
card play because the STS2 API changed between branches.

The two files exist only because STS2 currently has two parallel public
branches with a small API difference. Once STS2 promotes v0.104.0+ to
its public stable branch, this stable file will be re-released against
the new API and the two files will collapse back into a single
download. If you don't run beta opt-in, this is the only file you
need.

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What pressing Z does

• Single-step undo — pops the most recent snapshot and restores the exact combat state at the moment before the last card / potion / end-turn was played
• Turn-level undo — Shift+Z rewinds all the way to the start of the current player turn in one go
• In-combat undo button — a ↶ Z button appears next to the energy display; clicking it does the same thing as pressing Z
• Combat-only — the undo system is active inside an active combat. There is no undo on the map, no undo after a death animation finishes, and no undo across screens
• 30-snapshot history — up to 30 prior states per combat are kept in memory; older snapshots are dropped silently

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How it works

The mod takes a deep snapshot of the combat state the moment any of
these actions begin:

• Card play (PlayCardAction)
• End turn (EndPlayerTurnAction)
• Potion use or discard (UsePotionAction, DiscardPotionGameAction)

Pressing Z pops the most recent snapshot and restores:

• HP, block, and energy
• Hand, draw pile, discard pile, exhaust pile (including order)
• Powers and stack values on every creature
• Relics, potions, and orbs
• Monster intents for the next turn
• RNG state — so the next draw plays out the same way it would have
• Visual state — spine animations, modulate, hitboxes, and hover-tip focus all reset to match the restored frame

This is a snapshot approach, not a command/inverse-op approach.
Picking the inverse of every status interaction in StS2 (Vulnerable
applied via X relic vs. via Y power vs. via Z card-on-hit, etc.) is not
realistic, so the mod captures-and-restores instead.

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Hotkeys

• Z — Undo one step (last card / potion / end-turn)
• Shift+Z — Undo to the start of the current turn

You can also click the ↶ Z button that appears
next to the energy display.

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Main features

• Single-key undo — one hotkey for the most common case (last action)
• Turn rewind — Shift+Z for full-turn rollback when you want to re-plan the entire turn
• Localized undo button — in-combat button, English / Korean tooltip
• Death-safe — the death animation completes normally; you cannot undo across the death frame
• Lightweight capture — relic capture uses the game's own MutableClone instead of a full reflection deep-clone, so per-card-play overhead stays near zero
• Visual fidelity — revived enemies, Centipede-style corpses, and hover-tips all restore correctly; no lingering "DEAD" overlays or stuck nameplates after undo
• Power state fidelity — subtype-specific power fields (Kaiser Crab Boss back-attack facing, etc.) round-trip cleanly so visuals and damage multipliers don't desync after undo
• Cost-modifier fidelity — cards that pick up CardEnergyCost._localModifiers from Pounce (猛扑), Unrelenting (무자비), or Havoc now round-trip cleanly across undo so a "next attack/skill costs 0" effect re-applies after rewinding the card play that consumed it
• Phase-transition fidelity — TestSubject (실험체) phase 1 → phase 2 plays the proper vanilla transition animation instead of the regular death animation, single-target hover targeting keeps working on the reused NCreature node, and the HP bar reappears on phase 2 as expected (undo across the phase boundary is still unsupported by design)
• Revive-on-death minion support — minions with IllusionPower (환상) such as EyeWithTeeth (이빨 달린 눈) no longer freeze the game on death. Vanilla's revive flow runs unmodified, single-target hover targeting works on the reused NCreature after revive, and a post-revive HP-bar reconciler corrects vanilla's inconsistent AnimateOut/AnimateIn lifecycle so the bar reliably hides on death and reappears on revive (undo across the death itself is still unsupported by design)
• Necrobinder Osty support — Osty (골골이) with DieForYouPower no longer re-dies and vanishes on its 1-HP next-turn revive. The full death/revive cycle runs vanilla — die animation plays correctly during the dying-pre-revive window, and undo across an Osty death/revive correctly restores the body's alive/dead visual state to match the snapshot
• TheObscura (HIVE) freeze fix — the boss's IllusionMove minion summon no longer freezes combat when undone; phase / spawn-on-death logic stays on the vanilla path
• Inspect-screen softlock fix — undoing in combat no longer poisons the shared NInspectCardScreen instance. Previously, the orphan- card sweep that runs each undo would QueueFree the screen's internal NCard, and later — when you reached a merchant or any card-reward screen and right-clicked a card — the inspect overlay would throw ObjectDisposedException on every render and refuse to close, requiring a force-quit. The sweep now skips NCards owned by a Screen-class ancestor, so the inspect screen survives any number of in-combat undos
• NPower signal-duplicate error fix — the "Signal 'mouse_entered' is already connected" Godot ERROR no longer appears on every undo. Power refresh used to manually re-invoke each NPower's _Ready after the container rebuilt; Godot had already fired it once when the new NPower entered the tree, so the second invocation double-connected hover signals
• Right-click upgrade preview — in-combat right-click on a hand card to preview its upgraded version no longer locks input or freezes the preview state. Snapshot capture is gated behind an RMB-window check so synthetic preview-driven actions don't accidentally trigger snapshots. v0.0.8 adds a Godot.Input.IsMouseButtonPressed polling fallback so the gate still works on STS2 v0.103.2 in cases where the card UI consumes the RMB event before our _Input prefix sees it
• Small-enemy death pacing — Toadpole (올챙이) and similar small enemies' "lying dead" tail is trimmed so the corpse disappears at the same pace as the cinder dissolve VFX, not 1–2s after

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Installation

1. Download Sts2UndoMod-v0.0.12.zip from this page
2. Extract the two files inside (Sts2UndoMod.dll and Sts2UndoMod.json) into the mods/Sts2UndoMod/ folder inside your Slay the Spire 2 installation
3. Launch the game
4. Start a combat — pressing Z after any card play, potion use, or end-turn will undo it

The mod writes a small log to
%APPDATA%\Sts2UndoMod\probe.log on
Windows (or ~/.config/Sts2UndoMod/probe.log on
Linux/macOS). Attach this when reporting issues.

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Requirements

• Slay the Spire 2 with mod support enabled
• This file is built against the stable STS2 branch (v0.103.x). If you have opted into the STS2 beta in Steam → STS2 → Properties → Betas, download the -beta file instead — the stable dll will throw MissingMethodException on the beta branch because of an STS2 API change
• Auto-dormant in multiplayer — when you join a co-op (Host / Client) run the mod detects it and stops capturing snapshots; the ↶ Z button doesn't appear and the Z hotkey becomes a no-op. Leave the mod installed when you play with friends — you don't need to disable it before joining a lobby. Solo runs are unaffected

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Source & license

• Source: https://github.com/ing-gom/sts2-undo-mod
• MIT licensed