A photo of Nintendo's floor at E3 was leaked by Nintendo Enthusiast yesterday and it seemed to show off a new game known as Mario Maker.
The image, as you can see, features the old 8-bit era of Mario gaming. With a name like Mario Maker as well as the appearance of a stylus, it seems safe to assume that the game would allow customizable levels.
Also in the background you can see several characters with their Super Smash Bros art. Of course Smash Bros is the most anticipated upcoming Nintendo game, so it is no shock to see it so prominently featured in Nintendo's E3 area.
Mario, more than any other Nintendo series, lacks customization. Most Mario games involve what Nintendo wants you to play, leaving very little room for creating your own characters or levels. If this picture is real, the game would certainly be a nice change of pace to the Mario formula.
One thing we do know is that Nintendo is scheduled to give a 90 minute conference at E3 that will be dedicated to an unannounced 3DS title. It would seem that if this image is actually a leak, that Mario Maker could definitely be the focus of that conference.