What could be the plot in a 'Harry Potter and Merlin's Castle' fanfiction?

Perhaps a powerful and corrupted spirit that guards Merlin's Castle and sees Harry and his friends as intruders. This spirit might have its own evil agenda and try to stop Harry from achieving whatever goal he has in the castle, like obtaining a powerful artifact or knowledge. It could use all sorts of dark magic and illusions to deceive and harm them.

Well, it could be about Harry using his magic in a new and creative way to build a castle. Maybe he's tired of Hogwarts and wants to create his own place. He might use spells like Wingardium Leviosa to lift the stones and Protego to protect the construction site.

Well, it could be about Harry Potter discovering some long - lost magic that was once taught by Merlin. Maybe he stumbles upon an ancient spellbook or a hidden place where Merlin's teachings are preserved.

One possibility could be that Merlin uses his ancient magic to sense Harry's plight. He decides to take Harry under his wing, perhaps hiding him in a magically concealed place. Merlin then starts to teach Harry magic in a much more in - depth and different way compared to Hogwarts. Harry might learn spells that have been long forgotten in the wizarding world of his time.

One possible plot could be that Merlin, having been dormant for centuries, is awakened in the world of Harry Potter. He could then use his ancient magic to help Harry and his friends in their fight against Voldemort. Maybe he teaches them spells long forgotten, giving them an edge in the battle.

The plot could involve Harry exploring the castle's secrets. Maybe he discovers hidden chambers filled with ancient spells and artifacts left by his ancestors.

One possible plot could be that a dark wizard has taken over Windsor Castle and is using it as a base to plan an attack on the wizarding world. Harry and his friends must infiltrate the castle, which has been magically fortified, to stop the evil plan. They might discover ancient magic within the castle's walls that they can use to their advantage.

Perhaps the fanfic's plot involves a character who is unknowingly Merlin's apprentice. They start having strange dreams about Merlin guiding them. As they explore these dreams, they learn skills like time - traveling magic which Merlin was known for. They then use this ability to go back in time and change certain events in the wizarding world's history for the better, all while trying to keep it a secret from the other Hogwarts students and faculty.

Well, it could be about a new character in the Harry Potter world who has the powers or the role similar to Merlin. Maybe this new character uses magic in a way that combines the traditional Harry Potter magic with the ancient and powerful magic associated with Merlin. For example, they might be able to perform spells that are long forgotten in the wizarding world but were common during Merlin's time.

Another possible candidate in fanfictions could be Neville Longbottom. He has a deep connection to the magical world and shows great courage and growth throughout the series. His latent magical abilities, which are finally fully realized, could be interpreted as him being an heir of Merlin in a way. He has the potential to be a great wizard, just like Merlin was.