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 include blue spade platforms, red heart platforms, green club platforms, and magenta diamond platforms. The icons on the blocks will disappear over time, and the platform itself soon after. Only four platforms may be on screen at one time, and placing another results in the first platform placed disappearing.

If another player steps on the platform with the icon still on it, it will spit out three coins and a star meter on the GamePad will have a section filled. Standing on ten platforms will fill the meter entirely, and as a result a Boost Star appears; by tapping the Boost Star on the GamePad, the player enters into Super Boost Mode, allowing them to instantly defeat enemies and hit blocks by tapping them for a limited time, similar to a Starman.

Boost Mode is not limited to platforms, however, as the player using Boost Mode can also stun/damage enemies by tapping them, which can be done repeatedly to keep them from attacking. Additionally, 3-Up Moon Blocks (which will release a 3-Up Moon after being hit and then remain solid) can only be seen on the GamePad player's screen, and become usable for the other players only after being tapped; the block will revert after about 5 seconds, after which it can be hit again.

If the player manages to collect ninety-nine Extra Lives, the Boost Blocks become Mini-Boost Blocks.

Effects if touching an enemy
Here are the effects when touching an enemy in Boost Mode: If a Boo is touched from Circling Boo Buddies, it'll pause for a second and will quickly float back to its position.
 * Goomba and its variants, Monty Mole, Porcu-Puffer,- jumps backward
 * Koopa Troopa, Buzzy Beetle, Spiny- retreats to its shell
 * Dry Bones, Bony Beetle- collapses
 * Waddlewing- jumps in air/jumps and starts to glide if it is in ground/drops Super Acorn
 * Hammer Bro. and its variants- trips and cannot attack
 * Piranha Plant and its variants (pipe)- retreats to its pipe
 * Piranha Plant and its variants (ground)- cannot attack
 * Bob-omb- fuses
 * Foo- disappears then reappears
 * Lava Bubble, Spiny Egg, Gūrindai- does another jump
 * Swooper- swoops down
 * Amp and Big Amp- loses its electricity for a while, and can be stomped
 * Blooper, Mecha Cheep, Torpedo Ted, Rocky Wrench, Cannonball, Lakitu, Boo and its variants, Dragoneel and Baby Dragoneel, Skewer, Thwomp and Super Thwomp- pauses
 * Mecha Koopa, Rocket Engine- deactivates
 * Targeting Ted- explodes
 * Cheep Cheep and its variants- swims/jumps to the other way
 * Balloon Goomba- its balloon pops if the balloon is touched
 * Para-Beetle- flies down
 * Heavy Para-Beetle- flies up
 * Clampy- opens its mouth when closed
 * Grrrol and Mega Grrrol- rolls to the other way

Boost Rush
New Super Mario Bros. U features a mode similar to Coin Rush from New Super Mario Bros. 2 called Boost Rush. In Boost Rush, the player will play through a series of levels grouped together in packs, and the objective is to play through autoscrolling levels and collect the most coins, lose the least amount of lives, and make or beat the best time. The speed of the scrolling will increase every ten Coins while Star Coins worth 20 coins each. Unlike Coin Rush, though, the player has limited lives and can gain more by collecting coins or extra lives, although all players share the same lives, and the player using Boost Mode can pop any players in bubbles. When a player is playing Boost Rush, Miis can be seen in the background, supporting the players.

In the Penguin Pack, the Ice Flower is replaced by the Penguin Suit.

Trivia

 * The icons on the blocks spawned via Boost Mode are the same as the four symbols used to sync the Wii U console and GamePad during the system setup.