Correlated randomness in Slay the Spire 2

Researchers have confirmed that Slay the Spire 2’s random number generators are correlated, leading to predictable outcomes in specific game scenarios. This discovery impacts players’ understanding of randomness and strategic planning, especially for those using certain relics or encountering specific events.

The correlation was identified through analysis of the game’s beta version (v0.107.0), revealing that multiple RNGs, which are supposed to operate independently, instead exhibit predictable relationships. For instance, choosing Neow’s Bones relic in Underdocks results in a high likelihood (~54%) of receiving the Debt curse, a pattern that is consistent across many runs. This pattern is linked to how different RNGs are seeded and interact within the game’s code.

Specifically, the game uses multiple pseudorandom number generators (RNGs), each initialized with different seeds based on a hash of their event names and the overall run seed. However, due to the linear nature of the RNG algorithm used (C#’s System.Random), their outputs can become correlated when their seed differences are known, allowing skilled players or researchers to predict certain outcomes based on initial RNG results.

This phenomenon, known as correlated RNG (CRNG), was previously observed in the original Slay the Spire, but the current version’s design was expected to mitigate this issue. Instead, the analysis indicates that some correlations persist, notably affecting relics like Neow’s Bones and certain event outcomes, which can now be more reliably predicted.

Impact of RNG Correlation on Gameplay Strategies

This discovery matters because it alters the perceived randomness of the game, giving players with technical knowledge an advantage in predicting certain outcomes. It also raises questions about fairness and game design, as some players may experience less variability than intended, especially in scenarios heavily influenced by these RNGs. Understanding these correlations can influence how players approach relic choices and event strategies, potentially leading to more deterministic gameplay patterns.

Previous RNG Issues in Slay the Spire and Current Findings

The original Slay the Spire faced similar issues with RNG predictability, where multiple RNGs initialized with the same seed produced correlated outputs. Developers attempted to address this in the sequel by initializing RNGs with different seeds based on hashed event names. However, the recent analysis indicates that the underlying RNG algorithm’s linearity still allows for correlations, particularly when multiple RNGs are seeded close together or follow predictable patterns. The beta version’s code and seed handling are central to these findings, which are based on detailed testing and code examination by community researchers.

Extent and Impact of RNG Correlations on All Game Content

While the analysis confirms correlations in specific scenarios, it is not yet clear how widespread these effects are across all game content or whether future patches will fully address the issue. The precise impact on high-level gameplay and competitive play remains to be seen, and further testing is ongoing.

Developer Response and Potential Patches to RNG Handling

Developers are expected to review the game’s RNG implementation and may release updates to reduce correlations, improving randomness and fairness. Community researchers plan to conduct further tests across different game versions and scenarios to map the full extent of the issue. Players are advised to stay informed about upcoming patches that may address these concerns.

Key Questions

How does RNG correlation affect my gameplay?

It can make certain outcomes more predictable, such as curses from Neow’s Bones or event rewards, potentially giving an advantage to players who understand these patterns.

Will this issue be fixed in future updates?

Developers have acknowledged the issue and are investigating solutions, but no specific patch timeline has been announced yet.

Does this mean the game is rigged?

Not necessarily. It means that some randomness may be more predictable than intended, especially in specific scenarios, but core gameplay remains largely based on chance.

Can I still enjoy the game despite this issue?

Yes, many players continue to enjoy the game. Awareness of RNG correlations can help experienced players adapt their strategies.

Source: Hacker News