Correlated randomness in Slay the Spire 2

Recent analysis by the Slay the Spire 2 community has confirmed that the game’s multiple pseudorandom number generators are correlated, affecting the predictability of certain game outcomes. This discovery, based on testing the current beta version, reveals that knowing the result of one RNG can help predict others, impacting gameplay strategies and relic value.

The key finding is that Slay the Spire 2’s RNG system, which utilizes multiple seeded pseudorandom generators, exhibits correlation between its outputs. This correlation means that specific game events, such as the curse received from Neow’s Bones relic or potion drops in early fights, are not entirely independent but influenced by shared seed states. The community’s testing, primarily on beta patch v0.107.0, shows that these correlations can skew expected randomness, making certain outcomes more predictable than intended.

For example, players observed that choosing Neow’s Bones in the Underdocks map often results in a high likelihood (~54%) of receiving the Debt curse, contrary to the expected distribution. Similarly, the first fight’s potion drop rate varies significantly between maps, with a 76% chance in Underdocks and only 4% in Overgrowth, depending on the RNG seed. These effects are linked to the way the game initializes and uses multiple RNGs, each seeded with a hash-based seed plus specific identifiers.

Game developer statements are not yet available, and the community analysis is based on empirical testing and reverse-engineering of the game’s code, which is simplified in the discussion. The issue appears to be inherent to the game’s RNG initialization process, where multiple generators initialized with related seeds produce correlated outputs, reducing the randomness’s independence.

Impact of RNG Correlation on Gameplay and Strategy

This discovery matters because it reveals that some game outcomes are more predictable than previously thought, affecting player strategies and relic value assessments. For example, the high likelihood of receiving certain curses from Neow’s Bones could influence relic choices and risk calculations. Moreover, understanding these correlations can lead to better optimization of runs or exploitation of RNG patterns, which may alter the competitive landscape and casual play experiences.

Additionally, this finding raises questions about the fairness and design of randomness in Slay the Spire 2, prompting developers to consider whether the RNG system needs adjustment to ensure truly independent and unpredictable outcomes. For players, awareness of these correlations can inform more informed decision-making, especially in high-stakes runs or speedruns.

Previous RNG Issues in Slay the Spire Series

The phenomenon of correlated RNGs is not new to the Slay the Spire community. In the original game, players documented that multiple RNGs shared the same seed, allowing for pattern prediction and strategic manipulation, as detailed in a blog post by Forgotten Arbiter. To address this, Slay the Spire 2 introduced multiple RNGs seeded with different values, aiming to reduce predictability. However, recent community analysis indicates that the current implementation still exhibits correlation, likely due to the way seeds are derived from the initial game seed combined with string hashes.

This ongoing issue underscores the complexity of designing truly independent RNG systems in games, especially where multiple random events are involved. The current beta patch’s code, which uses hash functions combined with the seed for each RNG, appears to still produce correlated outputs, as demonstrated by the observed predictable patterns.

“The correlated RNGs mean that knowing the outcome of one can help predict others, which was not supposed to happen in a properly randomized system.”

— Community researcher on Hacker News

Extent and Impact of RNG Correlation in Full Release

It is still unclear how widespread or impactful these RNG correlations will be in the final, stable release of Slay the Spire 2. Developer commentary or official patches addressing this issue have not yet been released, and community testing is ongoing. The full extent of how these correlations influence high-level gameplay, speedrunning, or competitive play remains to be seen.

Developer Response and Potential RNG System Revisions

Next steps include monitoring official statements from the developers regarding this issue, as well as further community testing to quantify the impact across different game modes and scenarios. Developers may release patches to modify RNG initialization or seed generation methods to eliminate correlations. Players and content creators are advised to remain aware of these findings, especially when analyzing RNG-dependent strategies.

Key Questions

How does RNG correlation affect gameplay in Slay the Spire 2?

It can make certain outcomes, like curses or potion drops, more predictable, potentially influencing player decisions and strategies.

Is this issue intentional or a bug?

It appears to be an unintended consequence of the game’s RNG seed initialization method, not an intentional feature.

Will the developers fix this RNG correlation problem?

There has been no official statement yet, but community analysis suggests that fixing may involve revising seed and RNG initialization code in future patches.

Does RNG correlation impact competitive or speedrun categories?

Potentially, as more predictable RNG outcomes could influence run consistency and fairness, but the full impact is still being evaluated.

Source: Hacker News