Super Mario Galaxy/Dusty Dune Galaxy

Dusty Dune Galaxy is accessible from the Bedroom observation dome. You need 29 Stars to enter.

Star 2: Blasting through the Sand
There is a Hidden Star on this level. For the time being, do not feed the Hungry Luma.

Star 3: Sunbaked Sand Castle
There is a Hidden Star on this level. For the time being, do not collect any musical notes you may find.

Star 4 (Speedy Comet): Sandblast Speed Run
This Star is available when a Prankster Comet is in this Galaxy.

Do the same as for Star 2, only within a 4 minutes and 30 seconds time limit.

Star 5 (Purple Comet): Purple Coins in the Desert
This Star is available when a Purple Comet is in this Galaxy.

Star 6 (Hidden): Bullet Bill on Your Back
Enter Star 3 and proceed as for that Star until you reach the planet with the spiky plant. Ground Pound the tree stump on this planet and collect all the musical notes that appear. Use the Launch Star to reach a new planet.

Star 7 (Hidden Green): Treasure of the Pyramid
This is one of the three Green Stars, which you need to collect to unlock the Trial Galaxies.

Enter Star 2. Feed the Hungry Luma 20 Star Bits.