Slay the Spire 2’s RNG links rolls, Mega Crit investigates

A community analyst using the name tckmn published a technical breakdown showing that Slay the Spire 2 links multiple random outcomes so rolls that should be independent influence one another. The behavior appears in the game’s early-access build 0.107.0.

The report identifies several concrete cases. In the Underdocks region, the Neow’s Bones relic grants the Debt curse more than half the time, while in the Overgrowth region Debt cannot appear and Writhe is more common. Large Capsule shows different rarity mixes for its first relic by region and appears about 1.65 percent of the time in the Underdocks. For the Defect character, the first evoked orb in the Underdocks targets the leftmost enemy roughly 75 percent of the time in the first fight. The Trash Heap event currently yields a 0 percent chance to receive Rebound in single-player on build 0.107.0. Multiplayer results can vary with player Steam IDs because of how the random stream is seeded.

The underlying cause appears to be how the game generates and consumes random values in C#. The ordering and use of values create a single stream where one draw can change the distribution of later draws. That pattern is described as correlated randomness, or CRNG, by the analyst.

Mega Crit has acknowledged the issue and is investigating. Community manager Demi Montes told a community creator that the bug “is at the top of their priority list.” The studio has not published a technical postmortem or a timeline for a fix.

The analyst provided two written observations in the breakdown. One reads, “It is hard to express how instantaneously my brain automatically dismissed them as textbook confirmation bias.” Later the analyst added, “I am confident that Mega Crit will address the issue. For one thing, Spire 2 is still in early access… It would be pretty unreasonable, for example, if it was impossible to complete the in-game compendium.”

The correlated randomness affects initial relic and curse choices, in-combat targeting, event card pools and other systems where the game performs multiple random draws. The pattern is similar to a previously reported issue in the first Slay the Spire, but community members report it is more visible in the sequel because it influences many early and high-impact choices.

No release date for a patch has been announced. The game remains in early access while the developer investigates the reported randomness patterns.