The four players in NSMBWii is that complex? Given that games like Conduit and Mario Kart Wii have 12-person online... but then again, Brawl supported up to four and that had some bad lag. Given that Brawl depends a lot on accuracy, where Mario Kart Wii deals with its lag by making attacks and positions less precise, NSMBWii seems to depend on accuracy as well, from what I've seen.