One idea could be that Percy turns into a dragon to fight a powerful sea monster. Since he has his connection to water, as a dragon he could breathe a sort of water - based fire or ice that freezes the water around the monster, trapping it.
One possibility could be that Percy, as a new god, would have to deal with the complex politics of Olympus. He's always been an outsider, and now he'd be thrust into a world of power plays and ancient rivalries. Maybe he'd try to change some of the archaic rules that the gods have held onto for centuries.
Perhaps Percy turns into a falcon. In this form, he could soar through the skies and spy on his enemies from above. He might use his falcon eyes to find a secret lair of a villain or to track the movements of the Titans. It would also give him a different perspective on the world around him, seeing things from a bird's - eye view.
In a 'Percy Jackson turns evil' fanfiction, he might use his powers against his former friends. For example, his control over water could be used to flood Camp Half - Blood. His knowledge of the demigod world would also be a weapon in his hands to outwit and defeat those who oppose him.
Well, in the fanfiction, if Percy turns into a baby, he would probably lose all his skills and knowledge at first. But he might still have some instinctual connection to water. Maybe his friends like Annabeth would have to take care of him. She'd be really protective and try to find a way to turn him back.
In the 'Percy Jackson turns into a cat' fanfiction, he could end up in some really interesting situations. For example, he might be chased by some of the magical creatures at Camp Half - Blood that don't recognize him as Percy. His senses would be heightened as a cat, so he could detect things like danger or hidden treasures more easily. Also, it would be hilarious to see how Annabeth reacts when she first sees Percy as a cat. She might be confused at first but then try to figure out how to turn him back.
One great 'Dragon Percy Jackson Fanfiction' is 'The Dragon's Bond'. It's about Percy encountering a dragon that has a mysterious connection to his demigod powers. The story is full of action as Percy tries to figure out the dragon's origin and how it ties to his destiny in the world of demigods.
It depends. Some Percy Jackson fans might be really into this kind of fanfiction as it combines two exciting elements - Percy Jackson and dragon riding. However, compared to the more mainstream Percy Jackson stories, it may not be as widely known. There are a lot of different fanfiction out there, and popularity can vary greatly depending on the specific fan community and how well it's promoted among Percy Jackson enthusiasts.
One change would be his interests. Instead of just focusing on Greek mythology and his demigod adventures, he now has an additional passion for dragons. He might start spending his free time reading dragon lore.