Maybe Harry is turned into an elf by a misfired spell. Then he has to deal with his new small size and pointy ears while still trying to attend Hogwarts classes. He might face challenges like fitting into his regular robes or being taken less seriously by some students.
One possible fanfiction could involve Hermione being turned into an elf due to a misfired spell. In this scenario, she might struggle with the new form's limitations, like being shorter and having less physical strength. But, being Hermione, she would use her intelligence to adapt and find a way to reverse the spell. For example, she could search through ancient magical texts in the Hogwarts library to find a solution.
It could be Voldemort. He might see turning Harry into an elf as a way to weaken him. Since elves are generally seen as lower in the wizarding hierarchy, Harry in this form would be less of a threat to Voldemort in the eyes of many wizards.
It could be Draco Malfoy. Maybe he somehow manages to use a new spell or a dark object to turn Harry into a ferret out of spite. He might then try to keep Harry in that form to humiliate him in front of the whole school.
Maybe it starts with a strange magical experiment gone wrong in Hogwarts. Harry is curious and gets too close, and suddenly he's a baby. The story could then focus on how the teachers, especially Dumbledore, deal with this situation. They might try to figure out if this is a new form of dark magic they haven't seen before. And Harry, as a baby, would have no memory of who he is, so it could also be about his friends trying to make him remember bits of his past life.
Perhaps an old enemy of Harry's family resurfaces. This villain might have a long - standing grudge against the Potters and sees turning Harry into a baby as a form of ultimate revenge. They could be using a spell that has been passed down through generations in their family, a spell that was created specifically to harm the Potters.
Another plot could involve Harry's friends' reactions. Some might be very accepting and helpful, while others could be confused or even act differently towards 'her'. This could lead to some interesting character development and story arcs for both Harry and his friends.
Perhaps there's a plotline where the transformation into a ferret has some unforeseen side effects. For example, Harry might gain some ferret - like abilities such as enhanced sense of smell or speed, which he then uses to his advantage in solving a mystery or escaping from a dangerous situation in Hogwarts. He could also struggle with some of the more ferret - like instincts, like being tempted to hoard shiny objects.
In the 'Harry Potter gets turned into a cat' fanfiction, there could be a lot of comical situations. Imagine Harry trying to attend classes as a cat. He might jump on desks, knock over ink bottles, and cause chaos in the classroom. His professors would be very confused about this strange cat's behavior. And when it comes to fighting Voldemort, it would be a very different scenario. He might use his cat - like agility to dodge spells, but also have to find a way to cast his own magic in this new form.
It could be Voldemort. He might see Harry's new snake form as a way to either use him for his own evil purposes or as a threat to his power. Since snakes are often associated with Slytherin and dark magic, Voldemort might try to control Harry.