Even though Super Mario 64 came out in 1996, it still sees play today through the use of emulation. That's probably not too surprising considering the surge of retro-gaming we have seen lately but the ability to modify the SM64 ROM is also a big draw.
Whole forums exist on hacking Super Mario 64 and of course, it didn't take long for someone to make a two-player version. However, two players were not enough for modders Kaze Emanuar, Melonspeedruns and Marshivolt. Together, these three industrious enthusiasts created Super Mario 64 Online which allows up to 24 people to play the game together over the Internet.
In their introductory video (below), they admit that it is "more players than you'd even want," but the option to have that many people in the game at once opens new avenues of gameplay never before considered.
Obviously, you can play cooperatively but you can also compete against each other racing through levels (or fighting and pushing each other off platforms). Best of all, you can invent your own games and do whatever you want within the virtual world.
"We played hide and seek in the mansion," the mod team admits.
There are several characters from the Mario universe to play as, each with different abilities. For example, Princess Peach can fly for short distances (Super Mario Bros. 2, anyone?) and Luigi can sprint.
Do note, however, that you may encounter some hiccups. The core game was never intended to be multiplayer so glitches can be expected. It is also a bit tricky to get set up and connected with other players. There are options in the menus that need tweaking and IP addresses to be entered before you can start the game although this one-minute tutorial should help.
If you want to give Super Mario 64 Online a try, download and install the files from Google Drive or Discord. If you need people to play with, you can check out the SM64O forum or the game's Discord channel.