This page offers a guide on the Going after Guppy Power Star, which is the first level of the Sea Slide Galaxy. This galaxy is found in the Engine dome and requires 36 stars to unlock.
You’ll start the level off by landing on an island with peguins complaining about an Orca named Guppy whos taken over the area. To start the main objective you’ll want to swim up to Guppy and speak to him. Guppy will then challenge Mario to follow him around the course.
Swimming through the Eight Rings
Guppy will begin to start swimming and behind him occasionally a numbered ring will appear. Start swimming and aim to pass through each ring. You can use your spin attack while submerged to swim quicker. There’ll be a red shell that you can use to traverse your way through this level, making it easier to control and pass through the rings.
You simply need to follow Guppy on his path through the level with no need to overtake him. There will be hazards like Whirlpools and Gringills that can be easily avoided when following Guppy.
Once you have made it through all the gates, Guppy will provide a Mario with a Power Star that will be placed on the island you first started on. If you don’t make through all eight gates, you’ll end up losing a life.