Super Mario Galaxy 2/Freezy Flake Galaxy

Star 1: Bowser on Ice
Goal: Burn the giant Bowser ice sculpture with Fire Mario

On the starting planet, get the Fire Flower, run to the underside of the planet and burn the Goomba ice sculpture. A launch star will appear. On the next planet, get another Fire Flower, go down to the Bowser ice sculpture, and throw three fire balls at it. Touch the midway flag, and then you will find yourself falling down a slide with a row of coins for about five seconds. When you fall out of the slide, you'll be on the next planet. 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 ice sculpture on the middle platform is what you burn to get the Power Star. Go across all the snow platforms until you get to the one with the Fire Flower, then throw a few fire balls at the Bowser sculpture, and you'll get the Power Star.

Comet Medal
The Comet Medal is on the planet after you fall out of the slide. Destroy a few snow cubes and you'll find it.

Star 3 (hidden): The Chimp's Skating Challenge
Goal: Beat The Chimp's ice skating game record

Select Star 1 and on the second planet, burn one of the Goomba sculptures with Fire Mario to reveal a hidden warp pipe. Then 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. If you beat it, your award is a Power Star.