It supports up to 10 players
Modder CraftyBoss managed to do something that probably should have been done a long time ago: a Super Mario Odyssey multiplayer mod.
Housed on their Discord server, the mod (which requires a modded Switch) allows up to 10 people to play Mario Odyssey together, with different costumes to differentiate everyone: that actually sync while playing. The mod itself is a work in progress, as is the custom game mode concept, but for now, the basics seem to be working.
Interestingly, moon collection (collectibles that dictate game progress) “is shared between all players.” Meaning, you could have an entire crew jump into a level, and either play it separately to divide and conquer, or hang out together and go for the same objective. It reminds me of Castlevania: Harmony of Despair‘s core gimmick (man that game needs to come back on modern platforms!).
While Mario Odyssey felt more than complete on its own, something like this, even if it was just a few players at a time, gives it new life. “What if [X] had multiplayer” is something people have been pondering for decades in the realm of gaming, and mods have typically been the way to deliver on that dream.