Super Mario Galaxy/Sea Slide Galaxy

Sea Slide Galaxy is accessible in the Engine Room with 36 Stars.

Star 1: Going after Guppy
Swim up to Guppy and talk to him. Follow him and go through eight rings that he makes. Collect a shell on the way to make it easier. Once you have gone through all the rings, collect the Star he releases.

Star 3: The Silver Stars of Sea Slide
For the time being, ignore the Hungry Luma you meet on this level.

Star 4 (Cosmic Comet): Underwater Cosmic Mario Race
Grab a red shell. Use three rings to boost your speed. Jump out of the water and find the Star behind a building. You might want to throw away the shell (by spinning) to allow a long jump once on dry land.

Star 5 (Purple Comet): Purple Coins by the Seaside
100 coins, no time limit. All up high (Bee Mario - use short bursts rather than continuously holding down A to get from cloud to cloud) or on ground - none in water.

Star 6 (Hidden): Hurry, He's Hungry
Enter Star 3. Proceed through the level as for Star 3. When you meet the Hungry Luma, feed it Star Bits.