Whenever the player shakes the Wii Remote, Rock Mario makes uncountable rocks appear out of nothing, and makes himself into a boulder with help of those rocks. As a boulder, Rock Mario rolls at incredible speed, crushing any enemy in his way, and cannot stop until hitting a thick wall.
Why is Mario trapped inside a large boulder? That's the fault of the Rock Mushroom, which appeared in Super Mario Galaxy 2. What's better than rolling around at the speed of sound? Not much, but rolling around in a boulder that can destroy practically anything comes close... and that's something even Sonic could probably agree with! Somehow, even when encased in a tomb of solid rock, Rock Mario is still capable of jumping around! Just goes to show how much this plumber loves his platforming escapades.