Princess Peach has been kidnapped! Again! Everyone was celebrating the Princess' birthday when a giant birthday cake arrived... but then Bowser Jr. and the seven Koopalings popped out and kidnapped her! Mario, Luigi and two Toads make chase to rescue her once more. Will they succeed?

New Super Mario Bros. Wii is a continuation of the Super Mario Bros. games. As with the original, players jump, dash and grab power ups such as the Super Mushroom and the the Fire Flower, which lets them throw fireballs at their foes. New powerups have been added too - the Propeller Hat allows players to zoom vertically up in the air, and then glide back down, the Ice Flower lets players freeze enemies into icy blocks, and the Penguin Suit gives them traction on ice as well as allowing them to belly slide. Yoshi, from Super Mario World makes a return, as well - players can ride him and he'll eat enemies and berries in levels.

The Wii Remote's tilting feature is used to activate certain parts of levels - for example, jumping onto specific platforms and tilting the Wii Remote will angle the platform too. Another level has players aiming a light on a boat by using the Wii Remote so that they're not lost in the dark. Shaking the Wii Remote while wearing the Propeller Hat causes the player to fly straight up, while shaking it near objects picks them up or throws them.

The game has a special feature known as a 'Super Guide' - when a player dies eight times in total in a level, a special block appears at the start of the stage the next time they play. If the player hits this block, Luigi will take over and play through the level, showing them how to complete it. This allows players to progress through the game even if they are having trouble on a particularly difficult level.

Up to four players can play simultaneously. When playing together, as long as one person is on-screen in a level, players can keep returning in-game after they die by floating in a bubble which is then popped. If all players lose their lives, they are sent back to the map screen. Another mode, Coin Battle, has all players versus each other, with the aim being to pick up the most coins while heading toward the goal.