One plotline could involve a centaur animagus being hunted by a group of dark wizards who want to use their unique magical abilities for their own evil purposes. The centaur has to use both their centaur strength and their animagus form's stealth to evade capture and defeat the dark wizards. They might transform into a fox to hide in the bushes and then use their centaur archery skills when in their original form to fight back.
A possible plotline could be that a centaur animagus uses their transformation ability to spy on dark wizards. They could turn into a raven and fly unnoticed, gathering information to protect the wizarding world and the Forbidden Forest.
Another plotline might be that a centaur discovers they are pregnant as a result of some ancient magic being reawakened. The centaur then has to navigate their own traditional beliefs and values about pregnancy and family, while also dealing with the potential implications for the centaur - human relations in the Harry Potter world. They might seek help from certain characters in the wizarding world, like Hagrid, who has a connection to magical creatures, and together they try to figure out how to handle this unprecedented situation.
One interesting fanfiction could be about a centaur who discovers the ability to become an animagus. Maybe they transform into a majestic eagle to soar above Hogwarts and keep an eye on the students. This could add a whole new layer of mystery and protection to the wizarding world.
A possible plotline could be that Harry's horse Animagus form is discovered by the wrong people. For example, the Ministry of Magic might suspect him of using dark magic to achieve this form and he has to prove his innocence. This could lead to a whole adventure of him finding evidence and allies within the wizarding world to support his case.
Perhaps in a fanfic, Harry's phoenix Animagus form is discovered by Hermione while she is researching ancient magic. She helps him understand and control his new form. As a phoenix, Harry can access a hidden library within the Forbidden Forest, which contains knowledge that can defeat Voldemort once and for all. But he has to overcome various obstacles and traps set by dark magic to reach the heart of the library.
A really cool plotline could be a centaur - human friendship that defies the usual boundaries. For instance, a centaur befriends a student who is an outcast at Hogwarts. They help each other grow, with the centaur teaching the student about the magic of nature and the student introducing the centaur to the joys of human creativity and innovation, like new spells or potions.
One plotline could be that the female centaur is in danger, and Harry Potter comes to her rescue. Maybe she has some information about a dark wizard's plan, and the bad guys are after her. Harry uses his wizarding skills to protect her, and in the process, they form a strong friendship. Another could be that the centaur is an outcast among her own kind, and Harry, being an outsider in some ways himself in the wizarding world, helps her find her place.
A plotline could involve Harry using his Jaguar Animagus form to explore hidden parts of Hogwarts. He might find secret passages or rooms that are only accessible in his animal form. For example, there could be a hidden chamber beneath the Quidditch pitch that he discovers while prowling as a jaguar.
One interesting plotline could be Harry discovering his animagus form earlier than in the original series and using it to secretly explore Hogwarts at night. He might find hidden passages or secrets that were previously unknown.
A stag, just like his Patronus. It would be a powerful symbol of his connection to his father and his own inner strength.
A possible plotline could be that Harry's basilisk - related Animagus form is a result of some ancient magic that was dormant in him. The Ministry of Magic might see this as a threat and try to hunt him down. Meanwhile, Harry has to figure out how to use his new form to protect himself and his friends. He might meet other Animagi who have similar but different forms, and they could either help or hinder him. Along the way, he could also discover new spells or powers that are related to his Animagus form and use them to fight against the dark forces in the wizarding world.