Well, in a 'Harry Potter at Camp Half - Blood' fanfiction, the plot could be that Voldemort has made an alliance with some of the ancient Greek monsters. Harry, in his quest to stop Voldemort, stumbles upon Camp Half - Blood. There, he meets new friends and allies. He has to learn their ways quickly in order to face the combined threat. He might also find some ancient magic at the camp that could be the key to finally defeating Voldemort once and for all. This would involve a lot of character development for Harry as he adapts to a new environment and new types of magic.
One interesting plot could be Harry Potter arriving at Camp Half - Blood and being mistaken for a demigod at first. He then has to prove his own magical abilities which are different from the demigods'. As he stays, he starts to learn about the Greek gods and their ways, and he tries to find a way to combine his Hogwarts magic with the powers and knowledge at the camp. Maybe he could even help the demigods in a battle using his unique spells.
Yes, there are quite a few. You can find them on various fanfic websites. Some might focus on crossovers between the two universes, like a character from Harry Potter ending up at Camp Half - Blood and having to adapt to the new environment and its rules.
Another theme is the discovery of new magic. With the merging of two different magical concepts, fanfiction often features characters exploring new forms of magic that are unique to this combined universe. For example, spells that are a combination of Hogwarts magic and the powers of the demigods. This makes the stories exciting as readers get to see something new and different.
Some would be very curious. They've probably never seen someone like Harry before. Others might be a bit skeptical, wondering what his intentions are.
Maybe a story where the demigods have to face a new type of monster that is immune to their usual weapons and they have to find a creative way to defeat it. For example, they might have to use the environment in a way they never have before, like using the magic of the forest around Camp Half - Blood to their advantage. This would involve a lot of exploration and discovery within the camp's boundaries and its surrounding areas.
In such a fanfiction, Harry could discover the world of Greek mythology. Maybe he'd meet demigods and learn about their powers. He might also compare his magic from the wizarding world with the powers of the demigods at Camp Half - Blood.
Well, he might be really confused at first. The magic in the Camp Half - Blood is different from what he's used to at Hogwarts. He could make some new friends, like the demigods there. Maybe he'd learn new combat skills too.
A really cool plot could involve a prophecy that predicts the joining of the two camps. This could lead to some initial mistrust and rivalry among the demigods, but as they face common enemies and challenges, they start to bond and learn from each other. For example, the Camp Jupiter demigods could teach the Camp Half - Blood ones about Roman battle strategies, while the Camp Half - Blood demigods could show their counterparts some of their more unorthodox Greek magic.
One idea could be a quest that requires demigods from both camps to work together. Maybe they have to retrieve a powerful artifact that's being guarded by an ancient monster. The demigods from Camp Half - Blood could use their unique skills like Percy's water - based powers, and those from Camp Jupiter could contribute their Roman - style combat and discipline.
In certain fanfictions, a plot twist could be that the Half - Blood Prince was not a single person but a group of wizards working together. They had been leaving the notes in the potions book for a greater purpose. Another interesting plot twist might be that the Half - Blood Prince was actually an animagus and could transform into a creature that had a special connection to Voldemort's Horcruxes. This would add a whole new layer to the story. Also, there could be a plot twist where the relationship between Harry and Snape is completely different from the start. Snape is actually trying to protect Harry in a much more obvious way, but Harry misinterprets his actions because of the false reputation Snape has in the fanfiction world.
In some fanfictions, a great plot twist is that Harry himself has some hidden powers that are awakened during his sixth year. For example, he might gain the ability to communicate with magical creatures in a much deeper way. This could lead him to discover secrets about Hogwarts that even Dumbledore didn't know. And perhaps the relationship between the Half - Blood Prince and a long - lost relative of Harry's is revealed, which throws a whole new light on his family history and his role in the wizarding world.