This page offers a guide on grabbing the Shine Sprite in Episode 3 of Ricco Harbor. This area is accessed via the Rainbow M on the side of the Boathouse on the west side of Delfino Plaza once you’ve obtained at least 3 Shines and defeated the Polluted Piranha.
Chase Shadow Mario
Just as in the first Course, Bianco Hills, your task here is a simple one, Shadow Mario has resurfaced once again and you’ll need to give chase with FLUDD to put him down.
He’ll begin the level on the nearby boat, give chase and use the FLUDD to spray him a little before chasing him toward the chimney stack and hopefully striking him a few more times. From here, he’ll climb up to the blue platforms, you can reach this yourself by using Side Somersaults up the chimney stack and then use another followed by the Hover mode of FLUDD to reach him. Shadow Mario will spend the rest of the time running around this part of the harbor, keep up the chase and strike him to bring this Episode to a close and pocket another Shine.