Act 4 or The Ending is the fourth and final act of Slay the Spire.
Act 4 is a bonus Act that can only be accessed through repeated gameplay — it is not accessible until the player has beaten the game with every character minus the Watcher.
Unlike every other Act, Act 4 is unique in that it forces the player down a single path, which will always be the following rooms in order:
- A rest site
- A merchant encounter
- An Elite encounter against the Spire Shield and Spire Spear
- A final boss fight against the Corrupt Heart
The simple, predictable nature of Act 4 means that the player can build a deck around defeating the Corrupt Heart early in the game, as the only true source of randomness in Act 4 is what the merchant will sell.
Despite its predictability, Act 4 is easily the toughest Act for unprepared players; it contains a resting site placed against the player's favor, a notoriously difficult Elite encounter, one merchant, and what is arguably the strongest boss in the entire game.
This Act spans from floor 52 to floor 55, which is the final floor of a non-Endless game:
- Floor 52 is always a rest site.
- Floor 53 is always a merchant.
- Floor 54 is always an Elite encounter against the Spire Shield and Spire Spear.
- Floor 55 is always a boss battle against the Corrupt Heart.
How to access
To access Act 4, the player must first beat the game (defeat the Act 3 boss) at least once with the Ironclad, the Silent, and the Defect. Once this is done, the player will be able to access Act 4 and start collecting the required keys; an unfilled triangle will appear to the left of the player's name to indicate that they are able to collect the keys.
Note that beating the game with the Watcher is not required to access Act 4.
The Emerald Key is obtained by defeating a buffed Elite. A special Elite counter is marked with flames on the spire map and will only appear once per Act. Defeating a special Elite will reward the player with the normal Elite payout plus the Emerald Key.
The special Elite encounter will not appear again once the player has obtained the Emerald Key for the rest of the run.
The Sapphire Key can be obtained through any non-boss chest. The Sapphire Key is linked to the Relic that normally appears in the chest — the player may only take either the Relic or the Sapphire Key. Once the Sapphire Key is taken, it will no longer appear in non-boss chests for the rest of the run.
Entering Act 4
Once all three keys have been collected, the player must defeat the Act 3 boss to advance to Act 4.
If the player does not have all three keys, Act 4 will be inaccessible and the player's run will be forced to end, resulting in the normal Victory? screen.
None. Act 4 has no monster encounters.