A great plot idea could be that the heroes assemble from different magical schools around the world, not just Hogwarts. They come together to compete in a friendly but also dangerous magical tournament that tests their abilities to the limit, and in the process, they form unbreakable bonds.
One interesting plot could be the heroes from different Hogwarts houses uniting against a new dark wizard threat that is more powerful than Voldemort. They might have to combine their unique magical skills and knowledge.
Perhaps the heroes assemble to save a powerful magical artifact that is being targeted by a group of dark forces. Each character could bring their own knowledge and abilities to the quest. For example, Hermione's vast knowledge of spells and potions would be crucial, while Harry's courage and experience in facing dark wizards would lead the group. They might also encounter new magical creatures along the way that they have to either befriend or fight.
Hermione Granger would also be a main character. Her intelligence and vast knowledge of magic would be invaluable in any situation the heroes face. She could come up with strategies and solutions.
Another interesting aspect could be the origin stories of the villains in heroes assemble fanfic. A villain might have a tragic past that led them to their evil ways, and the heroes have to figure out how to stop them without just using brute force.
One idea could be Harry Potter arriving in Skyrim and using his magic to combat the dragons. Maybe he teams up with the local mages and they learn from each other's magical techniques.
One idea could be exploring what would happen if a new, mysterious student joined Hogwarts during the Triwizard Tournament. This student could have a hidden agenda related to the Dark Arts and start influencing the events of the tournament in unexpected ways.
One interesting plot idea could be Harry's return to Hogwarts as a teacher. He could pass on his unique experiences and knowledge to the new generation of students.
One idea could be a dragon that forms a bond with Harry and helps him in his battles against Voldemort. Maybe the dragon has some special powers that are crucial for Harry to win.
One idea could be Harry and his friends exploring new magical realms that were previously unknown. Maybe they discover a hidden school of magic that has a different approach to teaching spells.
Another plot could focus on the lives of the secondary characters from the original series. For example, Neville could be the head of Herbology at Hogwarts and discovers a new, dangerous plant that has some sort of connection to an ancient magic. The 'carry on fanfic' could then be about how he and his students deal with it, with some cameos from the main characters.
Well, a great plot for a Harry Potter mansion fanfic could be centered around a lost heirloom. The mansion was once owned by an important wizarding family, and a valuable heirloom has been lost within its many rooms and corridors. The characters embark on a quest to find it, facing various challenges like magical traps and puzzles. Also, the mansion could be a place where time behaves differently. People who enter might find themselves in different eras of the wizarding world, and they have to find their way back to the present while also uncovering the secrets of the mansion's past.