What Slay the Spire 2 Acts Change

This note answers a narrow question: do Overgrowth, Underdocks, Hive, and Glory change unknown rooms, events, enemies, elites, and bosses?

Short version:

• Acts change map length, unknown count, event pools, normal encounter pools, elite pools, boss pools, ancient pools, background, and music.
• Acts do not directly change the base odds for an unknown room becoming event, normal combat, shop, or treasure.
• So when unknown rooms feel different between acts, the main reasons are the number of unknown nodes and the act-specific event pool used after an unknown room becomes an event.

Two Meanings of Map

Players often use “map” for two different things:

Phrase	What it means	What it changes
“This act is Overgrowth / Underdocks / Hive / Glory”	The area, or act	Room count, unknown count, event pool, encounter pool, boss pool, and more.
“What will this unknown become?”	The room-type roll when entering an unknown node	Uses a shared base odds system that changes with unknown-room history.

Acts Change Event Pools

An unknown node first rolls a room type. Only if it becomes an event does the game pull a specific event from the event queue.

That queue is built from:

current act events + shared events - locked events

That is why event themes differ by act:

Act	Act-specific events	What feels different
Overgrowth	13	The largest event pool, with forest, plant, nest, carving, spring, and similar themes.
Underdocks	10	More underwater, dock, bath, whirlpool, and sunken-treasure themes.
Hive	10	More insect, fusion, flower, parasite, and lantern themes.
Glory	7	Fewer act-specific events, with training, trial, reflection, and tinkering themes.

There are also shared events that can appear across acts, such as The Merchant???, Crystal Sphere, Tea Master, Relic Trader, and The Future of Potions. Unlock progress can filter events out before they enter the pool.

Acts Change Monsters, Elites, and Bosses

Each act has its own encounter pools:

• Normal combat pulls from the current act's normal encounter queue.
• Elite combat pulls from the current act's elite encounter queue.
• Bosses are chosen from the current act's boss pool. If there are unseen bosses, the game prioritizes discovery order.

So a normal combat icon does not mean the same thing in every act. The same is true for elites and bosses.

Acts Change Map Length and Unknown Count

Acts also decide how many rooms, unknown nodes, and rest sites appear:

Act	Base room count	Unknown nodes	Rest sites
Overgrowth	15	about 10-14	about 6-7
Underdocks	15	about 10-14	about 6-7
Hive	14	about 9-13	about 6-7
Glory	13	about 9-13	about 5-6

In multiplayer, each act has one fewer base room.

This matters because even if the unknown-room roll rules are shared, the act still changes how many unknown rolls you can encounter.

Acts Change Node Distribution

Standard maps roughly follow these rules:

• The first normal row is fixed to normal combat.
• The row right before the boss is fixed to rest sites.
• A middle row is fixed to treasure; some effects can replace that treasure row with elites.
• Shops default to 3.
• Elites default to 5; the Swarming Elites ascension modifier increases that count.
• Remaining nodes are filled with the act's rest-site count, unknown count, shops, and elites; leftover nodes become normal combat.

The map generator also avoids several awkward layouts. For example, elites, rest sites, treasure rooms, and shops are restricted from appearing too directly adjacent to the same type.

Unknown Odds Are Not Act Tables

The base unknown-room odds are roughly:

Result	Base odds
Normal combat	10%
Treasure	2%
Shop	3%
Event	Remaining odds, initially about 85%
Elite	Disabled by default

However, it is not a fixed “85% event” every time. If a non-event result does not roll, its odds increase. If it does roll, that result resets to its base odds. Event odds are the remaining probability, so they fall as monster, treasure, and shop odds build up.

In practical terms: after several unknown rooms become events, later unknown rooms are more likely to become combat, shops, or treasure. Once combat rolls, combat odds reset.

These unknown odds are shared rules, not separate Overgrowth, Underdocks, Hive, and Glory tables. Acts affect the outer layers: how many unknown nodes you see and which event queue is used after an unknown becomes an event.

Route Planning Takeaways

• To see more act-specific events, path through more unknown nodes in that act; unknown nodes are not guaranteed events.
• Hive and Glory usually have slightly fewer unknown nodes than Overgrowth and Underdocks.
• If several unknown nodes in a row become events, later unknown nodes are more likely to flip into combat, shop, or treasure.
• Elite, boss, and normal combat difficulty depends on the act's encounter pools, not just the map icon.
• Unlock progress changes event and ancient pools; new profiles, older profiles, multiplayer, and mods can all change results.

Implementation Details

This section is implementation detail. Skip it if you only care about route planning.

At the code level, acts are defined by ActModel subclasses:

Act	Class	Main configuration
Overgrowth	Overgrowth	15 base rooms, 13 act events, 3 weak encounters, 3 boss candidates.
Underdocks	Underdocks	15 base rooms, 10 act events, 3 weak encounters, 3 boss candidates.
Hive	Hive	14 base rooms, 10 act events, 2 weak encounters, 3 boss candidates.
Glory	Glory	13 base rooms, 7 act events, 2 weak encounters, 3 boss candidates.

The default act list is Overgrowth, Hive, and Glory. Once Underdocks is unlocked, it can replace Act 1; if it has not been discovered yet, non-multiplayer runs prioritize showing it.

When the game generates room pools, it:

1. Combines the current act's AllEvents with ModelDb.AllSharedEvents.
2. Removes events that are still locked by timeline progress.
3. Shuffles the result into the act's event queue.
4. Generates normal encounter, elite encounter, boss, and ancient selections.
5. When entering an event room, pulls the next valid event and records visited events to avoid repeats when possible.

Standard maps are generated by StandardActMap. Map RNG is derived from the run seed with an act_N_map stream, so the same seed, act number, and game state tend to reproduce the same map structure and node distribution.

Unknown-room odds are maintained by UnknownMapPointOdds. The base values are normal combat 0.10, treasure 0.02, shop 0.03, elite -1, and event odds are computed as 1 - sum of positive non-event odds. After each roll, the rolled type resets to base odds and available unrolled types increase by their base odds.