This is a fun puzzle in a nice, calm beach land. When you water the flowers here, either they give you coins or they pop up a fun shape. If you do the one over to the left of the entrance, it makes a sandcastle. Run into the opening of the sandcastle to start the puzzle.

When you get to the first set of nails, the bottom left one is a one-up mushroom. Just run fast and it's pretty easy.

The next 2 nails are just 2 coins. Get to the main area and you should have plenty of time to first go to the one-up mushroom on one side, then over to the shine on the other.

Tip from ~mal~:
There is a hidden shine sprite in Gelato Beach. go to the dune bud that reveals stairs leading down to coins. Spray the back wall and a picture of the shine will appear. The shine will float to the top of the hill. Go get it and be happy!

Super Mario Sunshine Walkthrough