One possible plotline could be Harry using his knowledge of the wizarding laws, which he learned through his years at Hogwarts and his experiences with the Ministry of Magic, to defend wrongly accused wizards in a wizarding court. Another could be him trying to reform the wizarding legal system which he might find full of loopholes and biases.
One interesting plotline could be a wizard lawyer defending a wrongly accused magical creature. For example, a hippogriff that was attacked by a wizard but is being blamed for the incident. The lawyer has to gather evidence in the wizarding world, which might involve spells like Revelio to uncover hidden facts and interviewing witnesses like Hagrid who has a deep knowledge of magical creatures.
One possible plotline could be a private lawyer helping Harry Potter deal with the legal aspects of his inheritance from his parents. Maybe there are some dark wizards trying to contest it, and the lawyer has to use both magic and Muggle - like legal knowledge to fight for Harry's rights.
One possible plotline could be about the Weasley family trying to improve their financial situation. Maybe they come up with a new business idea in the wizarding world, like a magical product that becomes a huge success and changes their economic status. Another could be a story about how the Ministry of Magic regulates the financial system in the wizarding world, and there are some characters who try to manipulate or reform it.
Well, one possible plotline could be a story where a character from the wizarding world, perhaps a powerful wizard, takes on a concubine in a parallel world or an alternate version of the wizarding society. The concubine might be from a different magical culture and their relationship could cause political or social unrest within the wizarding community.
One possible plotline could be that the parrot is a magical pet of a new character who enters Hogwarts. This parrot has the ability to detect dark magic, so it helps the students in their fight against the forces of Voldemort.
One possible plotline could be Harry being secretly trained by an unknown figure to become an assassin against the dark forces. He would have to hide this new identity from his friends at Hogwarts.
A plotline could involve an Eldrazi being brought to Hogwarts by a dark wizard who wants to use its power for evil. The students then have to work together to contain it. Along the way, they learn about the Eldrazi's nature and find that it's not entirely what they expected. There could be some interesting character development as they face this new and powerful threat.
One plotline could be Naruto being a transfer student at Hogwarts. He might struggle to adapt to the magic system while also showing off his ninja skills. Another could be Naruto teaming up with Harry Potter to fight a common enemy that threatens both the ninja world and the wizarding world.
One possible plotline could be that Harry, after some dark magic influence or a strange accident, starts to show Joker - like behavior at Hogwarts. He might play cruel pranks on his classmates and teachers, using his magic in unexpected and unethical ways.
One possible plotline is that Broly is brought to the Harry Potter world as a result of a powerful spell gone wrong. He initially causes chaos with his strength but then gradually learns about the concept of magic and starts to respect it. Another could be that Broly is a hidden protector of Hogwarts, his Saiyan powers being the ultimate defense against a new dark force that the normal magic in the wizarding world can't handle.