Sandy Shine Sprite
From the Super Mario Wiki
Sandy Shine Sprite is the bonus tenth episode of Gelato Beach in Super Mario Sunshine. It can be accessed in any episode in Gelato Beach where the tower is accessible. This is the only bonus Shine Sprite that can be obtained during any episode, discounting the 100-Coin ones.
By spraying a Dune Bud next to the trampoline behind the tower, the player can find a staircase leading to some Coins. By spraying the wall at the end, the player will reveal an image of a Shine Sprite. Fully revealing the Shine Sprite image will cause an actual Shine Sprite to appear.