Every core Mario game had previously been a single-player affair, at most allowing a second player to join in and switch off as Luigi or grab a Wii Remote to help collect stars in Galaxy. But New Super Mario Bros. Wii changed that by allowing three extra players to jump in as Luigi and two Toads.

It was great fun, but the levels still felt designed around one player, and the extra co-op partners usually made things more chaotic and difficult rather than helping out.