For decades, two 3D Mario titles have stood on opposite ends of the spectrum regarding game design philosophy: Super Mario 64 (1996), the pioneer of analog, open-world exploration, and Super Mario Galaxy (2007), the masterclass of linear, gravity-defying spectacle. For years, fans have dreamed of a fusion between the two—what would it be like to explore Peach’s Castle with the spin mechanic and planetoids of the Wii era?

To play it, you do not download the game itself. You download a patch file (usually a .bps or .xdelta file) that is applied to a legally dumped ROM of the original Super Mario 64 (US version). Most search results that claim to offer the "full game" are illegal pre-patched ROMs, which are often packed with malware by bad actors.

You need a clean, unmodified dump of Super Mario 64 (USA) with the hash 3CE6A... (specific values vary by patch). You must dump this from your own N64 cartridge using a device like a Retrode or an Analogue NT. Pirating ROMs from the internet is illegal, but fair use for modding a game you own is a grey area often tolerated.