One possibility is that Harry Potter becomes a hybrid of a wizard and a centaur. He would inherit the centaur's knowledge of the stars and nature. His lower body being that of a centaur would make it difficult for him to move around Hogwarts in the normal way. He would have to find new ways to get to his classes. And he might be shunned by some students who are afraid of his new and strange appearance, but he could also form new alliances with those who are more open - minded and interested in his unique situation.
Maybe the Ministry of Magic could be the main antagonist. If Harry turns into a hybrid, the Ministry might see him as a dangerous abomination. They could try to capture him and keep him locked away, thinking that his new form is a threat to the wizarding world's order. They might not understand that Harry is still the same person inside and that his new form could actually be an asset in the fight against evil.
Well, perhaps the plot could involve Harry having some phoenix - like abilities. He might be able to heal himself quickly like a phoenix does when it rises from the ashes. He could also have a special connection to fire, being able to control it to some extent. And maybe he could communicate with other phoenixes in a way that helps him in his battles against the dark forces.
One possible plot could be that Harry is under a powerful dark spell. The transformation into a dragon might be a part of a scheme by Voldemort or his followers to either discredit Harry or use his new form for some evil purpose. Maybe Harry has to learn to control his dragon form in order to fight back and protect Hogwarts and his friends.
In this fanfiction, it could be that a magical accident occurs during a potion - making class. Harry accidentally drinks a wrong potion which transforms him into a baby. Dumbledore then decides to keep Harry at Hogwarts, with the teachers taking turns to look after him. Meanwhile, Neville could be the one who discovers a clue about how to reverse the transformation by observing some strange behavior of magical plants in the school's greenhouse.
In a 'Harry Potter turns to the Dark Side' fanfiction, the plot might involve Harry being influenced by a powerful dark object. For example, a cursed artifact that makes him see the Dark Arts in a different light. He could start to believe that the ends justify the means and that the Dark Side has been misrepresented all along. As he delves deeper into the dark side, he begins to turn against his old friends, thinking they are too naive and weak to truly change the wizarding world.
In the fanfiction, it could be that there is some ancient magic tied to Slifer that has a connection to Harry Potter. Maybe a hidden prophecy or a long - forgotten magical artifact causes the transformation. As Slifer, Harry might find himself in a situation where he has to communicate with other magical creatures in a different way. He could also face discrimination from some wizards who fear his new form, but also gain allies who recognize the potential of his new abilities.
The plot could involve the hybrid's discovery of their true identity. They might have been raised as a normal human in the Harry Potter universe, not knowing about their phoenix side. As they grow older, strange things start to happen. For example, they might have an unusual affinity for fire or be able to sense danger in a way that others can't. They then embark on a journey to discover their heritage. Along the way, they meet characters from the Harry Potter series who either help or hinder them. They might end up at Hogwarts, where they have to deal with the reactions of students and teachers to their unique nature.
In a 'Harry turns into a vampire' fanfiction, the story could start with Harry being cursed by a powerful and ancient spell that turns him into a vampire. His friends at Hogwarts are initially scared and unsure how to deal with him. However, Harry is determined to find a way to reverse the transformation. Along the way, he discovers that there are some positive aspects to being a vampire, such as heightened senses that help him in his detective - like investigations into the origin of the curse.
If Harry Potter turns into a heartless in fanfiction, it would be a huge change from his usual self. His relationships would be in shambles. Hermione and Ron would be shocked and try to bring him back to his old self. He could ally with the Dark forces not because he believes in their cause but just for power. He'd disregard the feelings of others, like the way he cared about the younger students in Hogwarts before. This would create a very dark and different version of the Harry Potter world we know.
One possible plot could be that Fem Harry is targeted by a dark wizard who wants to use her as a weapon in her basilisk form. She has to fight against this control while also trying to find a way to reverse the transformation. Along the way, she might discover new powers or abilities that come with being a basilisk, and use them to her advantage in her fight for freedom.