From Nintendo Direct:
Super Mario 3D World: For the first time ever, Nintendo has created a four-player Mario game set in a 3D world. The game, developed by the same team that created SUPER MARIO 3D LAND for Nintendo 3DS and the Super Mario Galaxy games for Wii, lets up to four players play as Mario, Luigi, Princess Peach and Toad. Each character has his or her own unique characteristics, and people can play cooperatively or competitively. The new cat transformation turns characters into adorable felines that can scratch enemies and even scamper up the flagpole at the end of levels. Transparent warp pipes add some new puzzle elements to gameplay. The game is scheduled to launch in December 2013.
Super Mario 3D Land was a great game that provided a much needed change from the side scrolling Mario games, it looks like Nintendo is hoping to provide even more changes through their transparent warp pipes and four players.