Super Mario Galaxy 2/Freezy Flake Galaxy

Bowser on Ice
On the starting planetoid, get the Fire Flower, run to the underside of the planet and burn the Goomba snow sculpture. A Launch Star will appear.

On this planet you'll find another Fire Flower and bunch of snow sculptures and snow trees you can destroy with fireballs. There is also a Lucky Cube next to where you land on the planet and you can reveal a green warp pipe to the hidden star by destroying the snow tree between Bowser and the frozen pond. To leave the area, get the Fire Flower, go down to the Bowser snow sculpture, and throw three fire balls at it. Touch the checkpoint flag, and then you will find yourself falling down a slide with a row of coins to the next planet.
 * First planet


 * Second planet

When you fall out of the slide, you'll see a square platform with a bunch of blocks in the center. Get yet another Fire flower and burn the snow cubes until you burn the cube covering the top of the warp pipe. Go down the warp pipe, and you'll be on the last planet.

The Bowser snow sculpture on the middle platform is what you burn to get the Power Star. Hit the checkpoint and make your way around to the Fire Flower. The fastest way is to go counterclockwise straight to it, but it may be easier to go clockwise as there are more platforms and they're closer together. You can make your way across the lava by either pushing snowballs out into the lava or spinning to hit them out. This creates temporary pathways of snow you can run across to get to far platforms. When you get to the platform with the Fire Flower, quickly jump back over to the steps up to the Bowser sculpture and throw a few fire balls at it before your power wears off, and you'll get the Power Star.
 * Third planet

Sorbetti's Chilly Reception
On the starting planetoid you'll find a Rock Mushroom on the cabin porch instead of a Fire Flower, but you still need to destroy the Goomba sculpture on the other side to reveal the Launch Star.

This time the path down the slide is blocked and you'll need to find five Star Chips hidden inside the breakable stuff on the planet to create a Launch Star. The Lucky Cube is still nearby where you land on the planet and the tree between the slide and the frozen pond still has a green warp pipe in it. Jump down to the main area where all the Li'l Brrs are and grab the Rock Mushroom so you can start breaking things to find the Star Chips. When you have them all, a Launch Star will be revealed that will take you to the next planet.
 * First planet
 * 1) In the Goomba sculpture right in front of the blocked slide.
 * 2) In the Goomba sculpture right behind the first one.
 * 3) In the tree with the Star Bunny next to it on the opposite side from the frozen pond.
 * 4) In the crystal at the bottom of the wooden stairs going back up to the upper part of the level.
 * 5) In the Goomba sculpture at the top of the planet where you first landed.

Here you'll be on a snowy platform where it's very foggy and the wind is blowing. There's hardly any visibility here, so go slowly so you don't run into any enemies. In the upper area, there is a green warp pipe if you go straight from the checkpoint flag that will take you to a room with three Lucky Cubes in it, and right after the big granite stone before you go down to the lower level you'll see a Star Bunny next to a wooden platform. Jump off the platform onto the coin below and you'll land in a secret area with three 1-Up Mushrooms and a mini Launch Star that will take you back up. When you're done collecting, slide down the slope to another checkpoint and a Shop Luma before the Launch Star that will take you to the boss.
 * Second planet

You'll land on a little planetoid where you can take the mini Launch Star to the main planet where you'll fight Sorbetti. Sorbetti is a large rolling snowball with a bright red nose. You need to spin and hit his nose three times to defeat him. He starts out rolling slowly and then gets mad and a lot faster after you get two hits in. You'll also need to dodge around the snow rocks as you're running from him. If he hits you, he stops and rolls the other way. Follow him for a bit until he runs over some snow rocks and reveals a coin to replenish your health. It's a little tricky to time when to run in for a spin on his nose when he's going his fastest, so keep running off to the side when he gets near you until you see his nose come around.
 * Sorbetti

The Chimp's Skating Challenge (Hidden Star)
In either of the first two stars, destroy the tree between the slide and the frozen pond with Fire Mario to reveal a hidden warp pipe. Down the pipe you will find yourself in a room with The Chimp and a small ice rink. Talk to The Chimp, and he'll tell you the game you have to beat his record on. You'll need to skate on the ice by spinning and run into the green and orange enemies as they pop up while avoiding the purple spiky ones. The green enemies are worth 10 points and the orange ones are worth 50, and if you can get 500 points or better, your reward is a Power Star. The patterns are always similar, so you can somewhat memorize them, although if you get all the orange guys, most of the green ones and don't run into any spiky plants you'll easily get a high enough score.

Green Stars
After breaking open the Bowser snow statue with fireballs, jump into the chute and slide around so you're on the ceiling. If you stay in the middle of the ceiling you'll run right into the first Green Star. After finding the green pipe in the snow squares and taking it to the lake of lava with the snow Bowser in the center, you can see the shine from the second Green Star across the lake to the right of the Bowser. Using the snowball on the platform you start out with the checkpoint flag, hit it over to the far platform with the Fire Flower on it going counterclockwise around the statue. Hit the snowball out behind the platform some more and go along the path until you can see the Green Star and jump to it.
 * Green Star 1 or 2

On the second planet, after putting the star pieces together and launching there, go past the checkpoint and look down the second path to the right for a Star Bunny in front of a wooden platform going off the side of the planet into nothing. Stand on the platform and you should see a coin spinning in the air below you. Jump onto the coin to go down to a secret area with three 1-Up Mushrooms and the Green Star.
 * Green Star 3