Mariomaniacs recently completed the astonishing task of reverse-engineering Super Mario 64 and making an unofficial PC version. It doesn't need an emulator or anything, it's just Super Mario 64 running on PC. Nintendo are less than wholly impressed with this technical feat, sending in their lawyers to try to shut down downloads. A wholly unsurprising conclusion to a whole lot of work.
This fan-made PC port requires you to provide a ROM of the N64 game, with the PC port coming distributed as an executable or source code you can compile yourself. Supposedly it's built on community efforts to decompile and reverse-engineering the original. Mario 64 has been unofficially on PC for years through emulators but not having to process the game through an emulator means the DirectX 12 version could reportedly run faster and smoother with less input lag, as well as with easy support for 4k and ultrawide resolutions.
TorrentFreak report that Nintendo's lawyers have been flinging copyright complaints against sites hosting the downloads, as well as some videos of people playing it. They say it's "an unauthorised derivative work based on Nintendo's copyrighted work." I've still seen some lives links but evidently Nintendo do not approve.
I cannot imagine anyone involved is surprised by this turn of events. Nor can I imagine Nintendo will ever succeed in removing it from the Internet, only in making it harder to find. The cat is out the bag, and the cat is Mario after picking up a Super Bell.