Super Mario Galaxy 2/Beat Block Galaxy

Step to the Beep
You're going to have to use your ear in this galaxy! Most of the blocks you'll be walking on are Beat Blocks. These are yellow and green blocks that swap every three seconds. For example, if you saw some yellow Beat Blocks and then waited three seconds, they would disappear and some green Beat Blocks would appear in a spot close to where they were. When you get to the pyramid at the end, collect all five Silver Stars and you'll earn a Power Star.

You will find a 1-Up Mushroom in your path on top of a yellow block near the Comet Medal, and another in a crystal on the purple platform right after that. The star is all about timing, so listen to the beat and jump from one color to the next on the third beat so you land on a solid block.

Silver Stars in Double Time (Prankster Comet)
This is exactly the same the Step to the Beep, except that everything is four times faster than usual. Follow the instructions on Step to the Beep, but remember it's going faster than usual. You can find a Yoshi in some of the crystals in the level, but it probably won't make it any easier unless you're using his infinite flutter trick. If you're having trouble with this level, stock up on lives and just try to make it from checkpoint to checkpoint. Find a good rhythm to go from one block to another right next to it with a jump. For instances where there are two blocks of the same color, add in a spin to save yourself. If you time it right, you can actually run onto the next block just before it appears and end up on top of it. You will also find 1-Up Mushrooms in your path where one was in the other star and on one of the sides of the pyramid at the end.

Green Stars
Right after the first time the platform goes off to the left instead of straight ahead, then turns back the front where a purple platform is with a crystal on its far left corner, you'll find the first Green Star. At the corner with the crystal, either triple jump off it to the star or backflip and spin. The star is out diagonally from the corner, so make sure to hold in the appropriate direction because missing the star means a fall to your death. At the end of the level you'll see the the second Green Star on the bottom level of the pyramid above the rightmost purple block as you come up to it. You can try triple jumping across the switching blocks, but it's much easier to just backflip and spin from underneath the star.