A 4chan user posted download links for four files—two NSP (Nintendo Submission Package) files and one 7z (7zip) archive containing two NCA (Nintendo Content Archive) files—which were apparently dumped from a Switch development kit.

The two NSP files are a Game Boy Advance emulator called “Sloop,” while the two NCA files in the 7z archive are a Game Boy emulator called “Hiyoko.” The Game Boy games themselves appear to be separate applications.

Both emulators are reportedly signed by Nintendo Europe Research & Development, a Nintendo subsidiary headquartered in Paris that previously developed the DS and Wii emulators for the Wii U Virtual Console, the emulators for Nintendo Entertainment System Classic Edition and Super Nintendo Entertainment System Classic Edition, and the GameCube emulation technology used in Super Mario 3D All-Stars.

Twitter user TrashBandatcoot posted several tweets about the leak, including screenshots of the emulators, as well as links to a Twitter account that published footage of each one in action. That Twitter account no longer exists, but an archive of the page is available.

Another Twitter user, Mondo_Mega, posted an alleged list of Game Boy Advance games tested on the emulator, as well as the four separate Game Boy game applications.

The list of games include:

Game Boy Advance

• Astro Boy: Omega Factor
• Car Battler Joe*
• Castlevania: Aira of Sorrow
• Castlevania: Circle of the Moon*
• ChuChu Rocket!*
• Drill Dozer
• Fire Emblem: The Sacred Stones
• F-Zero: Maximum Velocity
• Game & Watch Gallery 4
• Golden Sun
• Golden Sun: The Lost Age
• Gunstar Super Heroes
• Harvest Moon: Friends of Mineral Town*
• Kingdom Hearts: Chain of Memories*
• Kirby and the Amazing Mirror
• Koro Koro Puzzle Happy Panechu!*
• Kuru Kuru Kururin
• Lufia: The Ruins of Lore*
• Mario & Luigi: Superstar Saga
• Mario Golf: Advance Tour Mario Kart: Super Circuit
• Mario Party Advance*
• Mario Tennis: Power Tour
• Mario vs. Donkey Kong
• Mega Man Battle Network 5 – Team ProtoMan*
• Mega Man Battle Network 2
• Mega Man Zero 3
• Metroid Fusion
• Metroid: Zero Mission
• Mr. Driller 2
• Ninja Five-O
• Pokemon Mystery Dungeon: Red Rescue Team*
• Pokemon Pinball: Ruby & Sapphire
• Super Mario Advance 4: Super Mario Bros. 3
• Super Robot Taisen: Original Generation
• Tactics Ogre: The Knight of Lodis
• Wario Land 4
• WarioWare, Inc.: Mega Microgames!
• Yoshi’s Island: Super Mario Advance 3
• The Legend of Zelda: The Minish Cap

*Denotes a game that was previously in the ROM folder, but not in today’s leaked build.

Game Boy / Game Boy Color

• The Legend of Zelda: Link’s Awakening DX
• Qix
• Super Mario Land
• Tetris

The emulators also include references to EZ-Flash cartridges, which Nintendo has long regarded as an illegal game copier. ModernVintageGamer, a YouTuber and game developer at Nightdive Studios and Limited Run Games, noted that Nintendo internally recognizing EZ-Flash cartridges raises questions about whether the emulators were actually developed by Nintendo. But Twitter user OatmealDome noted that the Git repository used for the project indicates that the image of the EZ-Flash cartridge was added by a Nintendo Europe Research & Development employee–whose name and email address is listed—on August 7, 2020. While faking a Git repository and setting specific email addresses and names when making commits (a snapshot or milestone along the timeline of a Git project) is technically possible, doing so would apparently take a lot of time and effort. Traces of code in the Game Boy Advance emulator also appear to indicate it was co-developed by Panasonic Vietnam.

As for what this all means—the speculation is that these are emulators tested for an eventual inclusion in the Nintendo Switch Online subscription service, which currently features games across the Nintendo Entertainment System, Super Nintendo Emulation System, SEGA Genesis, and Nintendo 64 libraries. But whether that ends up true remains to be seen. Both Eurogamer and Nintendo Life reported in September 2021 that Nintendo was set to add Game Boy and Game Boy Color titles to Nintendo Switch Online, with the former also claiming that “other retro platforms are also on the cards.” Later that month, Nintendo announced the addition of Nintendo 64 and SEGA Genesis titles.