Boost Mode

Boost Mode is a new feature introduced in New Super Mario Bros. U, where the player with the Wii U GamePad can interact with the game, not by controlling a playable character, but by using the GamePad's touch screen to manipulate the current gameplay.

Boost Mode allows the GamePad player to place platforms in the game to help or hinder the other players. These platforms can be placed by tapping an empty/vacant area on the Touch Screen, and the platforms come in a variety of colors. They currently include blue spade platforms, red heart platforms, green club platforms, and magenta diamond platforms. If the player double-taps the platforms, they will shrink into coin platforms, and will spit out five coins when another player steps on them. The platforms will slowly disappear over time, or when a player steps on it, and will vanish entirely if a player hits it as if it was an average Brick Block.

Boost Mode is not limited to platforms, however, as the player using Boost Mode can also stun/damage enemies by tapping on them, which can be done repeatedly to keep them from attacking.

Boost Rush
A mode exclusive to Boost Mode appears in New Super Mario Bros. U named Boost Rush. Every level is playable, but are set in an autoscrolling fashion and the player (and preferably another) must make it through in the alotted time, using Boost Mode to help the player through.