Super Mario 64 is now playable with a friend. Just like you always wanted. Oh? You never wanted that?
Still, this video from YouTube user Skelux is pretty interesting. It shows two Marios running around together in Mario 64, sliding, swimming, and platforming together like bros. Luigi is probably green with envy at these twins.
With this mod the entire game goes multiplayer. Play online with someone, or as the video says, play controlling both Marios at once on your own. To try this out, simply apply this patch to the original 8MB ROM.