The game also removed a controversial Act 3 boss.
If you've ever felt like Slay the Spire 2 was being oddly consistent with some of its "random" outcomes, you may have been onto something. Mega Crit has revealed in the latest patch notes published on Friday (19 June), that the roguelike's RNG system was producing unintended correlations between events that were supposed to be independent, allowing certain outcomes to become partially predictable. The discovery has prompted a complete overhaul of the system, headlining a major update that also adds Steam Workshop support, a long-requested Bestiary, and significant content changes.
According to the developer, information from one part of a run could sometimes be used to narrow down outcomes elsewhere due to the way the game's random number generators were implemented.
Slay the Spire II
Release date: 5 March, 2026 (Early Access)
Platforms: PC (Steam), MacOS, and Linux
Developer: Megacrit
Why did Slay the Spire 2 overhaul its RNG system?
The issue first came to light after players began investigating unusual outcomes tied to Neow's Bones, eventually uncovering patterns that were not supposed to exist.
"It turns out that everyone complaining about receiving Debt too often from Neow's Bones was right!" engineer Ed wrote in the patch notes. "We did, in fact, have some unusual RNG problems."
Like many games, Slay the Spire 2 relies on pseudo-random number generators, or PRNGs, to determine everything from card rewards to event outcomes. Different systems within a run use separate generators, each derived from the run's main seed and intended to operate independently. Mega Crit later discovered that some of those generators were producing correlated results despite being intended to operate independently.
To illustrate the issue, the developer pointed to the relationship between a player's opening Act and the curse received from Neow's Bones. While both outcomes were generated separately, the underlying correlation meant that information from one roll could be used to narrow down possibilities for the other. In practice, this meant information from one part of a run could sometimes be used to narrow down possible outcomes elsewhere.
"Once knowledge of this exploit is out there, players are naturally incentivized to use it to play optimally," Ed explained. “We don't want to encourage rote memorization of correlation tables, as it is tedious and unfun.” To address the problem, Mega Crit has replaced the game's previous PRNG implementation with xoshiro256**, a more modern system that the studio says removes the detectable correlations. Or, as the developer put it: "Rest assured that your suffering is now truly random!"
Steam Workshop support officially arrives
The update also marks the official arrival of Steam Workshop support. While Slay the Spire 2 has included an integrated mod loader since launch, Mega Crit had deliberately avoided promoting mod support while continuing to refine the underlying tools. Until now, installing mods required players to manually download files and place them alongside the game's executable.
With Workshop integration now available, players can browse, subscribe to and automatically download mods directly through Steam, with those subscriptions syncing across supported devices. "We built STS2 with modding in mind, and the game has had an integrated mod loader from day one," the studio said. The addition should make it significantly easier for players to explore community-created content, while giving mod creators a more straightforward way to distribute their projects.
What is the new Bestiary in Slay the Spire 2?
The update also introduces the Bestiary, a feature many players had requested during the lifespan of the original Slay the Spire. Accessible through the Compendium, the Bestiary currently tracks monsters players have encountered, alongside their animations and movesets. Developer Casey explained that the feature was not added to the first game because there was no clear way to deliver broader worldbuilding.
With Slay the Spire 2 placing greater emphasis on narrative elements, creature presentation and environmental storytelling, the team decided the time was right to finally add it. The studio also plans to expand the Bestiary in future updates with additional details, including enemy statistics and lore.
Which boss was removed from Slay the Spire 2?
Finally, a major boss has also been removed from the game. Doormaker, an Act 3 boss that beta players may already be familiar with, has been removed and replaced by a new encounter called Aeonglass. According to Mega Crit, the decision followed ongoing concerns about the fight's complexity.
"While Doormaker had interesting micro decisions in the fight, he was over the complexity threshold of what we want and had lingering issues," the developer explained. Rather than continue refining the encounter, the studio opted to start over with a new boss built around its current goals for Act 3. The update also includes a reworked Infested Prism encounter, new Ancient relics, multiplayer adjustments, quality-of-life improvements, and extensive balance changes across every playable character.
More changes were outlined in the patch notes, which included some bug fixes, quality-of-life updates, and more. The full patch notes can be found here.
