Slay the Spire 2 patch fixes RNG bug after fan's 8-hour proof

Key Takeaways

• A dedicated player spent 8 hours documenting a pseudo-random number generator bug that correlated starting areas with curse outcomes
• Mega Crit confirmed the bug and patched it, noting the issue stemmed from how different PRNGs shared seed values
• The patch also replaces Act 3 boss Doormaker with Aeonglass and delivers significant balance changes

Mega Crit just patched Slay the Spire 2 to fix a random number generation bug that let players predict which curse they'd receive. The bug existed because a player named tckmn spent eight hours proving it wasn't in their head.

RNG complaints in roguelikes usually amount to nothing. Human brains are terrible at perceiving randomness. Anyone who has missed a 99% shot in XCOM knows the feeling of statistical betrayal. But this time, the community member was right.

What was the Slay the Spire 2 RNG bug?

The bug centered on Neow's Bones, a starting option that gives players two relics in exchange for a random curse. Some curses are harmless dead cards. Others, like Debt, can tank your entire economy. Players suspected the curse selection wasn't truly random.

Tckmn's investigation proved the suspicion correct. If you started in the Underdocks, Neow's Curse had a 54% chance of giving you Debt. That's not random. That's a pattern.

Why pseudo-random number generators failed here

Mega Crit explained the technical root cause. Like most games, Slay the Spire 2 uses pseudo-random number generators. You feed a PRNG a seed value, and it produces a predictable sequence of numbers. Feed it the same seed, get the same sequence. That's how seeded runs work.

The problem: different systems in the game fed different seeds to their PRNGs, but those seeds correlated with each other. The decimal that determined which Act 1 area you got also correlated with your Neow's Bones curse roll.

“If our act roll is >0.5 (we're in the Underdocks), then it's highly likely that our Neow's Bones curse roll will be <0.5, which cuts the potential curses you can obtain in half.”

— Mega Crit patch notes

The developers acknowledged tckmn's manifesto directly in the patch notes, calling it an "eight-hour descent into madness" without which "we wouldn't have caught the issue." They've now switched to a system that eliminates these correlations. "Your suffering is now truly random," the notes state.

New Act 3 boss replaces Doormaker

The patch brings more than bug fixes. Doormaker, the previous Act 3 boss, is gone. Mega Crit said the boss exceeded their complexity threshold and had "lingering issues" they couldn't resolve through iteration.

Replacing him is Aeonglass, a DPS-race style encounter. The boss pumps Wither curses into your hand that deal damage to you. The damage ramps whenever Aeonglass upgrades the curses. Players who stall will suffer.

Balance changes hit the Regent hardest

The Regent class received the most balance attention. Some cards got buffed. Monarch's Gaze is stronger. Others got nerfed. Reflect, a community favorite, took a small hit.

The full patch notes are available on Steam. Players on Ascension climbs should expect meta shifts as the changes settle.

Frequently Asked Questions

What was the Slay the Spire 2 RNG bug?

The bug caused correlations between game systems that should have been independent. Starting in the Underdocks meant a 54% chance of receiving the Debt curse from Neow's Bones, rather than a truly random outcome.

How did a player prove the RNG bug existed?

User tckmn spent 8 hours documenting patterns across multiple runs, eventually producing a detailed analysis that Mega Crit called an 'eight-hour descent into madness' and credited in the official patch notes.

Who is the new Act 3 boss in Slay the Spire 2?

Aeonglass replaces Doormaker. The new boss is a DPS race that pumps Wither curses into your hand, dealing escalating damage if you can't kill it quickly.

Is Slay the Spire 2 still in early access?

Yes, the game remains in early access. This patch is one of several major updates Mega Crit has released as they refine the sequel based on community feedback.

Source: PCGamer latest