As part of today's ARMS direct, Nintendo revealed details on the game's two online modes: Party Mode and Ranked.
Regardless of which mode you choose, you'll be dropped into a lobby that can support a staggering 20 players at once. It should be noted however, that hitting this number is achieved by using 10 consoles, each connected to two players each.
Once in a lobby you'll be matched up with other players to participate in a match. Several of these matches can all start at once in the same lobby, so rather than being stranded waiting for a match to finish, the odds are much better that you'll be having fun of your own. It's a great way to keep people hanging out in the lobbies longer and keep players engaged.
Ranked matches are a different animal entirely. Ranked matches are one-on-one only, and your performance dictates whether you'll rank up or lose points. Unfortunately that's all the detail that has been given so far. We'll have more as it develops.