Super Mario Galaxy 2 appears to give Mario the magical ability to walk on clouds. Judging by this image from the Official Nintendo Magazine, these are the happiest clouds ever. They love being stepped on!
It's clear that Mario's return trip to the stars will have no shortage of new (and returning) gameplay gimmicks. In addition to floating in the sky, it seems Mario can also turn into a boulder, ride dinosaurs, and drill through planets. The only thing he can't seem to do is his job. What happened to that plumbing gig you had, huh? This leaky pipe isn't going to fix itself, you know.