I "think" this is how Metroid Hunters works on Wi-fi...
You find people similar to the way you do in Mario Kart, by just letting it find random people for you. The matches are for up to four players and if I recall correctly... it's always first to 7 kills or whoever has the highest score after 7 minutes.
I think you can re-adjust the settings if you're playing with friends though, just gotta get their friend code first. Having the friend code also allows you to communicate via mic and text chat. You can also set rivals. This can be people you don't really like but want to face many times so you may be able to pummel them... or people you want to avoid because they can hand you your head on a platter.
Please note... Nintendo is still fixing up their Wi-Fi mode on Metroid Hunters. Many people cannot get four players in a game and their statistics chart is a little buggy. I'm not sure when they'll fix it, all I know is they're working on it.
You also get a few extra stats for your Wi-Fi record instead of just wins and losses... the only other one I can remember at the moment is "connection rating". This rating tells the player that are facing you if you're a cheapskate who disconnects if you're going to lose. So no mid-game disconnecting!!!
Well that's all I can really remember. Feel free to correct any of my undoubtedly large number of inaccurcies in that big of information.
I don't play this game online merely because I don't like the control style in the game. I probably won't ever play it.