Nintendo-Europe on 05 October 2013
Super Mario 3D World producer Yoshiaki Koizumi is working on something, but we don’t know what yet.
http://www.worldsfactory.net/2013/06/20/super-mario-3d-world-producer-will-announce-new-game-just-not-yet
http://tecnologia.elpais.com/tecnologia/2013/06/17/actualidad/1371473880_093710.html
It may be a 3D Mario game in the tradition of Super Mario 64.
