Rock Mario is a form in Super Mario Galaxy 2, first appearing in the Boulder Bowl Galaxy. Mario and Luigi can turn into this form when he touches a Rock Mushroom. By shaking the Wii Remote, Mario will transform into a giant boulder. In this form, Mario can roll around and jump, damaging enemies and big red crystals with items inside them. If Mario touches certain enemies or a wall, he will revert to his rock form, but can be turned back into a giant boulder if the player shakes the Wii Remote. Although Rock Mario can destroy Boulders, touching Chomps makes him lose his health and powerup. It is possible to turn back to normal by jumping and pressing . This can stop Mario from flying off an edge, but this move is disabled during the second mission of Melty Monster Galaxy.
The form later makes a small appearance in the Freezy Flake Galaxy where it was used to collect Launch Star pieces. The Melty Monster Galaxy, however, made extensive use of the power up in two of its missions. In the mission "The Chimp's Bowling Challenge", Mario had to use the Rock Mushroom to defeat Pinheads and score a total of 5000 or more points. In the galaxy's second mission, "A Stroll Down Rolling Lane", Rock Mario was needed to get across a large track to the Power Star.
In his "boulder" form, Rock Mario is almost unstoppable and has limited control over his movement in rolling. When the player manages to stop his rolling (while he is still a boulder), he will automatically escaped his boulder when the player does not move the control stick for a short period. Moving the control stick right after the boulder has stopped will make the boulder roll again.
Also, in the second phase of the final fight with Bowser in this game as well as Super Mario Galaxy, Bowser transforms himself into a boulder to attempt to roll and hit Mario, similar to Rock Mario's ability.
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