Act 4 or The Ending is the fourth and final act of Slay the Spire.
Overview[]
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.
An image of the Act 4 map. Notice the triangular symbol in the top left corner.
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 (floor 53 to floor 56 on Ascension 20), which is the final floor of a non-Endless game:
- Floor 52 (floor 53 on Ascension 20) is always a rest site.
- Floor 53 (floor 54 on Ascension 20) is always a merchant.
- Floor 54 (floor 55 on Ascension 20) is always an Elite encounter against the Spire Shield and Spire Spear.
- Floor 55 (floor 56 on Ascension 20) is always a boss battle against the Corrupt Heart.
No events occur in Act 4. As such, unless the player has specific relics such as 
Peace Pipe or 
Shovel, their options are limited to the rest site and the merchant's offerings.
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.
Keys[]
To unlock Act 4, three Keys must be collected throughout the course of a game: the Ruby Key, the Emerald Key, and the Sapphire Key.
Ruby Key[]
The Ruby Key is obtained by using the recall option at a rest site. Once the Ruby Key is obtained, the recall option will not be available until the next run.
Emerald Key[]
The Emerald Key is obtained by defeating a buffed Elite. A special Elite encounter 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.
Sapphire Key[]
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 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.
Monsters[]
Debuts[]
None. Act 4 has no monster encounters.
Elites[]
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