Slay the Spire 2's 'randomness' is broken, you're not just being superstitious

Slay the Spire 2 has a big problem right now, and you might not even want to spend too long looking into it if you're having a lot of fun with the year's landmark roguelike deckbuilder. That's because this issue, which developer Mega Crit is reportedly looking into as a top priority, relates to the way StS 2 handles many of its random outcomes. Given the inherently randomized nature of the game, that can have incredibly far-reaching implications. It also means that if you've been feeling oddly superstitious that a given roll goes badly more often than it should, you might actually be correct.

This so-called 'correlated randomness' (or CRNG for short) isn't completely new to the series, as it also affected the first game. At its core, the term refers to the way that the random number generation systems work in the code for Slay the Spire 2. The problem is that the way such numbers are shuffled in the C# programming language leads to situations where you can reliably connect certain outcomes together, allowing you to predict what will happen in one instance based on the state of another.

Enter hard-working Slay the Spire 2 analyst 'tckmn,' who has dropped an almost 7,000-word breakdown discussing exactly how CRNG is impacting randomness. They start with a very simple and striking example: the 'Neow's Bones' relic you can pick up at the beginning of a run, which grants you two other randomly chosen Neow relics and a 'random' curse. In reality, however, this roll is currently dependent on which Act One region you are in, to incredibly dramatic effects, as seen in the chart below.

That's right, you aren't dreaming it: you really do get saddled with Debt over half the time, at least in the Underdocks. Conversely, in Overgrowth it can't happen at all, and you're far more likely to end up with a Writhe in your deck. "People all over Reddit and Discord have been lamenting their terrible luck that they keep rolling Debt from Neow's Bones," tckmn writes. They even admit, "It is hard to express how instantaneously my brain automatically dismissed them as textbook confirmation bias. And yet…"

I mentioned up top that you probably don't want to dig too deep into the numbers here if you're currently enjoying the game, and that's because it will almost immediately lead you down a rabbit hole of rethinking every single choice you make. I'll give a few more basic examples to show you just how far this goes, but beyond that I'd advise caution.

In another early example, the first of the two relics given by 'Large Capsule' will never be common - it's about 70% uncommon, 30% rare in Overgrowth, but 37% uncommon, 63% rare in Underdocks. Sounds good for that latter option, but unfortunately, due to the impact of CRNG, Large Capsule only shows up "about 1.65% of the time" in Underdocks.

This isn't just limited to opening choices, either. When you're in the Underdocks as the Defect, there's a 75% chance your first evoked orb will hit the enemy on the left in fight one. How about the random cards from the Trash Heap event? According to tckmn, on the current 0.107.0 build, there is a 0% chance you can get Rebound in single-player. That's a big problem if you're trying to complete your compendium (and it isn't guaranteed in multiplayer either, as that randomness is influenced by your Steam ID).

I'm going to stop there, because I don't want to risk spoiling the whole game for you. The good news is that Mega Crit is apparently well aware of the issue. YouTuber Tristan 'FrostPrime' Dunham says he has spoken with Community Manager Demi Montes about the problem, and was told it "is at the top of their priority list." I have reached out to the team for additional comment, and will update the story with any response.

As for tckmn, they say, "I am confident that Mega Crit will address the issue. For one thing, Spire 2 is still in early access, much earlier in its development cycle than when CRNG was discovered in Spire 1. But also, compared to Spire 1, the influence of CRNG is much more directly impactful to players who don't know or care about it. It would be pretty unreasonable, for example, if it was impossible to complete the in-game compendium." The good news is that they believe a fix should be relatively simple, once the developer has settled on a solution. In the meantime, you can put your tinfoil hat in the trash.