These days, most high-profile games are impossible to play without purchasing. But Slay the Spire 2’s developers haven’t just bucked that anti-piracy trend: they’ve punt it into the stratosphere. And it all comes down to the deck-building game’s engine.
This is an oversimplification, but you can think of a game engine as the software developers use to build their games. By 2024, Slay the Spire 2 devs Mega Crit had already spent two years crafting the roguelike in Unity, a popular engine known for titles like Among Us and Hollow Knight. But the Seattle-based studio changed course after Unity announced that it would start charging developers every time someone downloaded their game. Unity eventually backtracked on this policy, but by then, Slay the Spire 2 was officially being built on another engine, Godot.
Godot doesn’t have the same brand recognition as a tool like Unreal Engine 5, but it has a few things going for it. One of the biggest differences is that the software is open-source. By proxy, Slay the Spire 2 is also open-source. In practice, this means that anyone with technical know-how can look into Slay the Spire 2‘s innards, AKA the source code.
This, by itself, is already an astounding fact. As of this writing, Slay the Spire 2 is one of the biggest game launches of 2026 — and anyone can see exactly how it was made. Most of the time, the public doesn’t get access to a game’s source code until a decade or two after launch… if it ever gets released at all. It is just as likely for developers and publishers to lose the source code outright, as we have seen for a number of retro games that didn’t get properly preserved.
The other notable consequence of Slay the Spire 2‘s Godot DNA is that, because anyone can look at and mess around with the source code, it is potentially easy to distribute the game without paying. Indeed, the early access title seemed to pop up on piracy sites almost immediately after launching. For some developers, the illicit sharing of a product that helps pay their bills would be grounds for concern. But Mega Crit seems completely unbothered by Slay the Spire 2‘s piracy situation.
In a Reddit thread where a user asked if the developer planned on preventing people from stealing its assets or code, Mega Crit lead programmer Jake Card had an unexpected response. “Honestly, we don’t really,” Card wrote. “We figure people who want to pirate it will find ways to pirate it, so there’s no reason to waste dev resources on it.”
In another Reddit thread, where someone pointed out that anyone could decompile Slay the Spire 2 to look at its source code, Card seemed perfectly content with the prospect. “It’d make me extremely happy to find out that other game developers learned something from reading through our code and our scenes :),” Card replied to a comment suggesting that Slay the Spire 2‘s open-source nature could be valuable for other game developers.
Earlier this year, Card explained that Mega Crit saw Godot’s open-source structure as a boon. When trying to port the game from Unity to Godot, issues could be resolved by picking apart the Godot engine itself. Eventually, Mega Crit built a custom fork of the engine that was geared to address Slay the Spire 2‘s specific needs.
“The open-source aspect remained a huge advantage as we got further and further into production,” Card wrote. “We never hit the sort of ‘dead ends’ you can hit with Unity when you just can’t find a solution to your problem.”
Even if people can download Slay the Spire 2 without paying for the game, there’s still good reason to do so. For some, it will be a matter of rewarding a developer for releasing a game that they can’t put down. For others, dropping cash for Slay the Spire 2 will make more sense because the pirated version of the game lacks multiplayer support — and that mode has its own unlockables and characters.