Well, a cool plot might be that Elsa's ice powers are actually a form of ancient magic that was lost in the wizarding world long ago. Harry and his friends figure this out and bring Elsa to Hogwarts to study her powers. Meanwhile, Anna follows and gets into all sorts of adventures at Hogwarts, like trying to fit in with the students from different houses. Also, the dementors could be attracted to Elsa's coldness, but instead of sucking out her soul, they end up getting frozen by her powers.
One idea could be that Harry and his friends get transported to a frozen wasteland during a spell gone wrong. They have to use their magic to survive the extreme cold and find a way back. Maybe they encounter magical creatures native to the frozen area that are both dangerous and helpful.
Some interesting Frozen 2 fanfiction plot ideas could revolve around the idea of a magical item. For example, there could be a magical crystal hidden deep in the forest that has the power to either save or destroy both the forest and Arendelle. Elsa and her friends embark on a quest to find this crystal before it falls into the wrong hands. Another idea is that a dark force from outside the known world tries to invade the forest and Arendelle, and the characters have to unite not only the people of Arendelle and the forest but also other magical beings to fight against it. Also, a plot could be centered around a prophecy that was never fully revealed in the movie, and Elsa and Anna must figure out what it means for their future.
A possible plot is that a dark wizard from the Harry Potter world tries to take over Arendelle. Elsa and Anna have to team up with Harry and his friends to stop this threat. The Frozen characters would be introduced to the concept of the Deathly Hallows and Horcruxes. Elsa's ice powers could be a key factor in fighting the dark magic. Maybe her ice can counter some of the dark spells, and together they all discover new ways to combine their unique abilities to defeat the evil wizard.
A great plot for Frozen fanfiction could be a time - travel story. For example, Elsa is sent back in time to when her parents were young. She has to figure out how to get back to her own time while also trying not to change the past too much. But she might also learn some secrets about her family's past and her own powers. Another could be a story about a competition in Arendelle. Anna decides to hold a magical - themed competition, and people from all over come to show off their skills. Elsa has to judge, and in the process, she meets someone who seems to have powers similar to hers but uses them for evil. Anna, Elsa and Kristoff then have to stop this person.
A great plot for a Potter Manor fanfiction could involve a mystery that surrounds the manor. For instance, strange noises at night lead Harry to uncover a long - forgotten chamber. It could also be about Harry restoring the manor to its former glory, perhaps with the help of Hermione's research on ancient magic used in the construction of such manors.
One interesting plot idea could be exploring what would happen if Harry had a different upbringing, like being raised by the Malfoys. It would completely change his view of the wizarding world and his relationships. Another idea might be a time - travel fanfic where Harry goes back to the Marauders' era and interacts with his parents and their friends. This could lead to him preventing certain tragedies or changing the future in unexpected ways. And then there's the concept of a fanfic where the roles are reversed, and Voldemort is the one trying to protect the wizarding world from a greater evil, with Harry being the main antagonist.
Perhaps Freddie creates a new web show that features interviews with Hogwarts students. This could lead to all kinds of adventures as they try to get the best guests and deal with the magical chaos that ensues. For example, they might accidentally release a magical creature on set.
One idea could be exploring the lives of the minor characters in the Harry Potter universe in an RPG - style adventure. For example, the story could follow Neville Longbottom as he discovers a hidden part of Hogwarts and has to face new magical creatures and challenges. Another plot could be a time - travel RPG fanfiction where a character goes back in time to change a crucial event in the wizarding world's history. Maybe they try to prevent Voldemort's first rise to power. A third idea is creating an RPG - style story where the characters have to compete in a new, dangerous magical tournament that's not the Triwizard Tournament, with different tasks and rules that test their magical abilities and moral compasses.
One idea could be that Mileena, with her unique fighting skills, is brought into the wizarding world by a powerful spell gone wrong. She then has to navigate Hogwarts, perhaps becoming a sort of unconventional Defense Against the Dark Arts teacher, teaching students her own brand of combat. Another could be that she teams up with Harry Potter to fight a new dark force that combines magic and the sort of otherworldly threats Mileena is used to in her own realm.
One idea could be that Supergirl lands in the wizarding world by accident. She might be initially confused by the magic there, but her superpowers could also offer a new perspective on magic. For example, she could use her heat vision to enhance a spell or her super strength to protect Hogwarts from a new dark threat that the wizards alone can't handle.