Dusty Dune Galaxy is accessible from the Bedroom observation dome. You need 29 Stars to enter.
Star 1: Soaring on the Desert Winds
Watch out for the two Dry Bones, then leap over the gap to the platform ahead. Although it may appear counter-intuitive, go ahead and leap into one of the tornadoes then perform a spin attack to turn into a mini helicopter-type thing. Now float over to the small platform ahead.Circle the platform to the far side and look for the warp pipe in the distance. Hover from tornado to tornado to reach it. After taking the warp pipe, you'll land on top of a huge stack of blocks. Give them a good ground-pounding to land at the bottom of the shaft.
Shortcut + Power-Up Shroom Position Mario on the right side of the shaft then perform a ground pound to come to a rest next to a secret tunnel. Crouch down and walk through it, then jump across the top of the Thwomp to the walkway. Up ahead are a trio of Thwomps who'll drop simultaneously. Run under all three as soon as they begin to rise and grab the Power-Up Mushroom at the end, then drop down the shaft. You can also wall-jump between the wall and the last Thwomp to grab a ? Coin, which reveals a ton of Star Bits.
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. There are no tornadoes.
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 take the same path that you took for that Star until you reach the planet with the spiky plant. If you don't see it at first, it's most likely because the sand has covered it. Wait a moment until the sand recedes and then Ground Pound the tree stump 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.