Super Mario Galaxy 2/Boulder Bowl Galaxy

Star 1: Rock and Rollodillo
Grab the Rock Mario power-up and head over toward the 6 creatures that look like bowling pins. Knock them all down, then proceed toward the ramp with a double-chevron on it. Roll towards the ramp and you'll be launched to another planet.

After defeating each of the rock-spitting creatures, a Launch Star will open, sending you toward a planet with Chain Chomps and Lodestones. Transform into Rock Mario again and roll towards the purple crystal containing a jump star.

Now on the golden translucent planet, tag the checkpoint flag and power-up with the Luma Shop before using the Launch Star to continue your journey.

Mini Boss: Rollodillo
On the wire mesh planet, you'll be faced with a Rollodillo.

Transform into Rock Mario and roll into the Rollodillo's exposed tail four times to defeat it. Avoid the spines and nose, as you'll not only lose your rock power-up, but also a life wedge with each collision.

Grab the Power Star and return to Starship Mario.

Star 3 (hidden): C'mere, Goomba
This Star is only available when you get a letter from Gearmo.

Enter Star 1 and find Gearmo in the level.

When you finish this level, Gearmo will appear on Starship Mario.