Well, 'Percy Horby's Unseen Journeys' is a fanfiction that I really like. It focuses on Percy's travels to unknown places and the people he meets along the way. The author does a great job of describing the new settings and cultures. And then there's 'Percy Horby and the Enchanted Forest', where Percy has to navigate through a forest full of magical creatures and solve various puzzles to get out.
One great Percy Horby fanfiction is 'Percy's New Adventure'. It takes Percy into a whole new world filled with magic and mystery that wasn't explored in the original. Another is 'The Hidden Side of Percy Horby' which delves deeper into his character, showing his insecurities and how he overcomes them.