Multiple prototypes for Nintendo Switch games have leaked online, including a demo for a cancelled game in development at Retro Studios. The prototypes were found in a Nintendo Switch dev kit and also include debug builds of Splatoon 2 and Arms, an unreleased LEGO Civilization game, and a Ridge Racer prototype.

Project Harmony is apparently what Retro Studios was working on in the intervening years between Donkey Kong Country: Tropical Freeze and Metroid Prime 4: Beyond. There have been rumors for years that Retro was developing a singing rhythm game or RPG, and this debug build, which is dated 2017, may have confirmed it. It was never officially announced.

It features a bubbly, red-haired female protagonist with a flower in her hair, who sings. The prototype features a playable test area and a bonus menu with concept art, dioramas, music, lore cinemas (presumably cutscenes) and the credits.

The protagonist uses a staff for a weapon and she can perform a ground slam, summon one of four magical creatures with varying abilities (one of which appears on the introduction screen), double jump and wall jump to climb platforms. The creatures include a winged sort of fish that she can mount and fly on, and a burly creature with moss on its back, which appears along with her on the title screen.

You can watch footage of the Harmony prototype here and here. It’s a real shame this was cancelled, it could have had much potential.

Source: Reddit

Update (April 8, 2025): Further footage of Project Harmony has been leaked onto Bluesky, in this thread. It shows some more polished combat, and a song that the protagonist sings with her animal friends.