If you’ve ever seen a Steam Deck playing a Legend of Zelda game, chances are you were seeing the Yuzu emulator at work. Now, Nintendo has sued the developers of Yuzu in US federal court, with the intent of squashing Yuzu for good.

In the lawsuit, spotted by Stephen Totilo, Nintendo alleges that Yuzu violates the anti-circumvention and anti-trafficking provisions of the Digital Millennium Copyright Act (DMCA) as well as accusing the creators of copyright infringement. It alleges Yuzu is “primarily designed” to circumvent several layers of Nintendo Switch encryption so its users can play copyrighted Nintendo games.

The company’s not only asking for the courts to stop Yuzu in its tracks with a permanent injunction. It also wants to take away its domain names, URLs, chatrooms, and social media presence; hand yuzu-emu.org over to Nintendo; and even seize and destroy its hard drives to help wipe out the emulator. Oh, and Nintendo wants lots of money in damages as well.

Aren’t emulators legal? Well… yes and no. While there’s legal precedent that suggests it’s okay to reverse engineer a console and develop an emulator that uses none of the company’s source code, those cases are roughly a quarter of a century old or more — it gets trickier when we’re talking about multiple layers of modern encryption and the copyrighted BIOSes that Yuzu and other modern emulators require to run.

The Dolphin Emulator for Nintendo Wii and GameCube got in enough hot water to abandon its plan to launch on Steam, when it was revealed that Dolphin ships with Nintendo’s Wii common key to help circumvent the copyright protection on Wii games. (Dolphin maintains that including that key is legal.)

Nintendo doesn’t allege that Yuzu includes any such keys, though. Yuzu takes a bring-your-own-BIOS approach, expecting users to either lift their own BIOSes and keys off a hacked Nintendo Switch (using a loophole that Nintendo eliminated in newer models), or more likely download a pirated one.

So instead, Nintendo’s arguing that Yuzu is knowingly “facilitating piracy at a colossal scale.”

As you’ll see in the full complaint below, Nintendo suggests that Yuzu is facilitating that piracy in myriad ways, including providing “detailed instructions” on how to “get it running with unlawful copies of Nintendo Switch games,” testing thousands of official Nintendo Switch games to verify their compatibility, and linking to websites that help users “obtain and further distribute the prod.keys.” Nintendo also says the developers have clearly extracted Nintendo Switch games themselves, bypassing encryption, in order to test their own emulator.

If Nintendo can prove that Yuzu is “primarily designed” to give people access to official Nintendo Switch games and has no other real use, Yuzu would indeed be in trouble. DMCA Section 1201(a)(2) bans products “primarily designed or produced for the purpose of circumventing a technological measure that effectively controls access” to a copyrighted work. It’s the same provision that game archivists have struggled with for years.

“The important thing is that Nintendo is bringing the case as a DMCA circumvention claim,” says Richard Hoeg, a business attorney who hosts the Virtual Legality podcast. He tells me that that while emulators are broadly legal if engineered “correctly,” the DMCA also lets Nintendo focus on whether the emulator was only designed to break Nintendo’s control over its games.

“There is a real chance for them to win as the court ‘tests’ things like the effectiveness of the measure and just how the emulator was created,” Hoeg says.

Nintendo suggests in its complaint that it may have actually been damaged by Yuzu, too, alleging that The Legend of Zelda: Tears of the Kingdom was illegally downloaded over a million times in early May 2023, while Yuzu’s Patreon membership doubled during that same period.

Legal emulation or no, Yuzu may not want to risk finding out in a court of law. Many small bands of developers have axed their projects after being approached by Nintendo, and it wouldn’t be surprising if Yuzu settled. “I’d say the claim here is enough to get a reasonable emulator company to cease, desist, and settle claims,” says Hoeg. “But remember that this is only one side of the story at present.”

Yuzu didn’t immediately respond to requests for its side of the story on Discord and via email. The team released Yuzu for Android last May.