Mermaid Sidequest

The Mermaid Sidequest is a small and not necessary sidequest in Phantom Hourglass. In it, you have to catch a fake mermaid in order to get a fishing rod.

To begin the sidequest, talk to the Old Wayfarer in Banaan Island. He will tell you about a mermaid who doesn't appear if monsters lurk nearby.

After that, you have to defeat every monster in the island, except for the ones in the caves, and the mermaid will appear by the coast. Every time you get near her, she will move away to other place.

You have to hit her with a boomerang and she will admit being a human dressed as a mermaid, Joanne, and will agree to go visit the old man that is interested in her.

Go to the Old Wayfarer's home, where he says he hasn't seen any mermaid. Ciela thinks the Joanne confused the Old Wayfarer with Linebeck. You have to talk to Linebeck where he says he saw her.

Go back to the Old Wayfarer's, where the [Old Wayfarer] and Joanne have already met. The Old Wayfarer says the he wants to give Link the old Fishing Rod he used to try to catch the mermaid.