Charizard is another one. A Charizard shapeshifter can bring in a lot of cool elements. It can be a powerful and intimidating presence, and when it shapeshifts, it might gain new abilities or appearances that are both fascinating and fearsome.
One idea could be a pokemon shapeshifter that is trying to hide its true form in a human - dominated city. It has to constantly adapt and learn human behaviors to avoid detection.
One plot idea could be Ash getting the ability to shapeshift accidentally. For example, he touches a strange Pokemon or an ancient artifact. Then he has to figure out how to control this new power while on his journey to become a Pokemon master. Another idea is that an evil organization wants to use Ash's shapeshifting ability for their own nefarious purposes, so he has to avoid them and protect his friends.
Obviously, Ash's main friends like Misty and Brock would be involved. Misty could be the one who first notices Ash's strange new ability and helps him keep it a secret at first. Brock, with his knowledge of Pokemon, could try to figure out how to reverse the shapeshifting if it becomes a problem. Also, Team Rocket would be great characters in this. They could constantly be trying to capture Ash in his different shapes, thinking they've discovered a new and valuable Pokemon.
One idea could be a Pokemon that can shapeshift into different legendary Pokemon to gain their powers. For example, it could shift into Mew to use its psychic abilities in unique ways. Another idea is a shapeshifting Pokemon that disguises itself as other common Pokemon to play pranks on trainers. It could be really fun to write about the chaos it causes.
A long - lost relative of Sirius Black could be a shapeshifter. Since the Blacks had many secrets and were involved in a lot of dark magic in their family history, it would be believable for a hidden relative to have this unique ability.
A unique character in a Pokemon shapeshifter fanfic could be a shapeshifting Pokemon that has a special bond with a particular trainer. This Pokemon can only fully control its shapeshifting ability when it's with that trainer. The trainer could be from a family with a special history related to Pokemon shapeshifting, and together they embark on a journey to discover more about this ability.
The Children of the Forest are also common in shapeshifter fanfictions. They are already somewhat mysterious in the original series, and their connection to magic makes them ideal candidates for shapeshifting in fan works. Writers might have them shapeshift into different animals or even blend in with humans to protect their secrets or fight against their enemies.
One great Hermione is a Shapeshifter fanfic is 'The Shapeshifting Hermione'. It has an interesting plot where Hermione discovers her shapeshifting abilities and how it affects her relationships at Hogwarts. The author does a great job of exploring the implications of such a power in the wizarding world.
Weiss Schnee can be a great character in shapeshifter fanfictions too. Her family's connection to the Schnee Dust Company could lead to some interesting plotlines where she shapeshifts to access hidden knowledge or powers related to Dust, perhaps into a form that can better manipulate Dust than she already can.