Every player has to have their own Switch console and copy of the game

The player who creates the room must be connected online throughout the play session

The other players who join the local room don't have to be online

There doesn't seem to be a way to play multiplayer in a single system with multiple controllers, you need multiple consoles (view edit below).

Edit

So I wanted to make this thread to clarify some details from the Direct as a lot of you are asking the same thing over and over in the other thread.Super Mario Maker 2 has three main game modes: the story mode, Course World, and Coursebot.Course World is where all the level sharing and multiplayer occurs and of course this mode is only available to Nintendo Switch Online subscribers. So yeah, leaderboards and Endless Challenge also require the subscription.In Course World there's the "Network Play" mode which involves multiplayer co-op and competitive play via internet and locally.You can play with online other people who also have NSO, but local play is a little bit more complicated:On the other hand, co-op making, part of the Coursebot mode, is only available locally, using a single system with multiple controllers. Also worth noting that while editing in Co-op you can't use dual Joy-con or the Pro Controller.Hope this clears out some of the confusion regarding NSO requirements for this game.: according to he eShop the game supports up to 4 players on a single system, but we know co-op editing is limited to 2 players, so maybe there could be single-console multiplayer at the end. It's currently unknown.