The statute of spoiler limitations should be over by now, but I’ll tread carefully: there is a connection between Super Mario Odyssey and Super Mario 64. I won’t say what that connection is, but it’s more literal than you’d expect from a usual Super Mario adventure. That connection seemed to spark some serious creativity in the rom modding community, in particular with a modder known as Kaze Emanuar. Kaze took a Super Mario 64 rom and somehow turned the game into Super Mario Odyssey. Since it’s a rom hack instead of a fan game, Nintendo’s lawyer ninjas might not assassinate it right away.
The name of the mod is as straightforward as it gets: Super Mario Odyssey 64. Kaze released a trailer along with the official release build, and it looks pretty impressive. Not only are the levels from Super Mario Odyssey “demade” in the Super Mario 64 style, Kaze and his collaborator Biobak64 arranged the soundtrack with the Super Mario 64 instruments and even got Cappy to work.
This mod obviously can’t be a full adaptation, but it does boast 80 moons. Kaze posted a trailer on their YouTube channel, which also includes links to a playthrough video, along with a download link for the patch and a tool to apply it.