A third plot idea might be based on the magic creatures. Suppose there was a fanfic where the relationship between wizards and magical creatures was reversed. Magical creatures became the dominant force in the wizarding world, and wizards had to fight for their rights and place. This would turn the whole Hogwarts and the wizard - witch hierarchy upside down.
Another idea could be a fanfic where the time - turner is used in a more extreme way. Instead of just going back a few hours, characters go back years and change major events. This could lead to a completely different wizarding world, like if Voldemort was stopped before he ever became powerful, and how that would affect the relationships and the magic society as a whole.
One interesting plot idea could be exploring what would happen if the Sorting Hat made different decisions for the main characters. For example, if Harry was sorted into Slytherin instead of Gryffindor, his entire journey would be radically different. He might have had different friends, different enemies, and a different approach to dealing with Voldemort.
Well, you could have a fanfic where Voldemort uses DND - style dark magic to open portals to other dimensions. The Order of the Phoenix has to quickly learn DND - style combat and magic rules to fight off the new threats that come through these portals. Harry could be sent on a special mission to find a DND - style mage who can teach them the counter - spells. Meanwhile, the Death Eaters are also trying to master this new form of magic for their own evil purposes. This would create a really exciting and unique story.
Perhaps a plot where the protagonist can choose to either side with the Ministry of Magic during a time of political unrest within the wizarding world or join a rebel group. This would involve different magical battles and moral dilemmas depending on the choice. In the 'harry potter cyoa fanfic', this could show different aspects of the wizarding society that we don't often see in the original books.
A cool plot for a Harry Potter Twilight fanfic could be a competition. The wizards from Harry Potter and the vampires and werewolves from Twilight compete in a series of challenges. These challenges could test both magic and the unique abilities of the Twilight characters. Or perhaps a love triangle between a Harry Potter character, a Twilight vampire, and a Twilight werewolf. It would be interesting to see how the different cultures and powers interact in matters of the heart.
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.
One idea could be that a dragon escapes from Gringotts and Harry has to use his skills to track it down. Maybe the dragon has a special connection to a powerful dark magic item that Voldemort was after.
One idea could be that Voldemort somehow enters the Runescape world to seek more power. Harry and his friends follow him there to stop him. They have to learn the rules of Runescape quickly to be able to fight Voldemort. Another idea is that a Runescape wizard discovers a portal to the Harry Potter world and brings some of the unique items from Runescape, like special runes, which causes a stir in the wizarding world.
A great plot for a Harry Potter academy fanfic might be a time - travel scenario. A group of students accidentally travel back in time to the founding days of Hogwarts. They have to navigate the different rules and attitudes of that era while also trying not to change history too much. Or perhaps there's a plot where a student is wrongly accused of a major crime at the academy and has to prove their innocence. They'll need to use their wits and the help of their friends to find the real culprit.
Perhaps in the fanfic, the snake is a key to unlocking an ancient magic that has been lost in the wizarding world. This could lead to a whole new adventure for Harry and his friends as they try to understand and use this magic.
One idea could be a fanfic where a character discovers a long - lost wand with a special power. For example, a wand that can open portals to different magical realms. The character then has to figure out how to use this power without getting into too much trouble with the Ministry of Magic.
One idea could be a crossover where characters from both universes meet. For example, Harry Potter could encounter Eragon and they could learn from each other's magic systems. Maybe Harry could teach Eragon about some of the more complex spells in the wizarding world, while Eragon shows Harry how to bond with a dragon in a more in - depth way.