The new Boost Mode for the New Super Mario Bros. U is a mode in which another player can take a certain amount of control by using the Wii U Gamepad. While up to four players progress through a level normally, the fifth player can use the game pad to add up to four blocks to the map or stun enemies.
This can be very helpful for newer players. Adding blocks can make it easier to traverse difficult areas, avoid certain enemies or even just simply make it easier to reach the top of a flagpole. The benefits for more experienced players can be just as aluring. While they may not need help getting through the level, these blocks can help them reach out of the way spots for hidden secrets or perhaps stunning an enemy in the right spot can provide a boost to the player's jump height that they need to reach an out of the way spot. Combining these two get can get you to a variety of places.
Interestingly, it's been noted (and may be obvious) that these features can also cause problems for other players. Perhaps you want to place a block just in front of someone before they jump or stun an enemy in a spot (like mid-air) that makes it difficult for an enemy to pass. At the end of the level, players swap controllers and it's the next person's turn to wreck havoc. Or instead, use the blocks to create challenges to be surpassed by friends.
