Mario gets shot out of a cannon and then can't stop running!
http://www.nintendoworldreport.com/news/31144
New Super Mario Bros. 2 will introduce new special stages called Dash Mario that basically transforms Mario into something like Canabalt or Bit.Trip Runner.
Mario is shot out of a cannon, and then will continue to dash until the end of the level. You have to time your jumps to collect coins and dodge obstacles.
In the Iwata Asks in which this was revealed, Nintendo President Satoru Iwata compared these levels to the mine carts in Donkey Kong Country.
To all those people saying Nintendo is making a cheap port, and not coming up with new interesting mechanics to these New Super Mario Bros...I would like an apology. It looks like Nintendo is in fact trying to create fun new mechanics, and classic Mario at the same time.
Perhaps the 3DS game may be more interesting than the WiiU game.