One great 'Percy Jackson Supernatural Crossover Fanfic' is 'The Hunters and the Winchesters'. It combines the world of Greek mythology from Percy Jackson with the demon - hunting of Supernatural in a really engaging way. The characters from both universes interact in a believable manner, and the plot keeps you hooked from start to finish.
When writing a 'Percy Jackson Supernatural Crossover Fanfic', it's important to balance the two worlds. Don't let one overshadow the other. You can introduce new characters that are a mix of both universes, like a demigod who was turned into a hunter. Also, research is key. Look into the different mythologies and Supernatural episodes to get inspiration. Build up the story gradually, starting with the initial encounter between the two groups and then leading to a big climax where they have to use their combined skills to save the day.
First, you need to understand the universes. For Supernatural, know about the different kinds of monsters, the lore of the hunters, and the Winchester brothers. For Percy Jackson, get familiar with the Greek gods, the demigods, and Camp Half - Blood. Then, think of a good reason for the crossover. Maybe a new threat that can only be defeated by the combined forces of both worlds. Start with a strong opening that grabs the reader's attention, like a sudden appearance of a Greek monster in a Supernatural - like town.
I really liked 'When Hunters Meet Demigods'. In this fanfic, the concept of how the hunters from Supernatural would react to the demigods in Percy Jackson's world is explored. It's full of action scenes where the skills of the hunters and the powers of the demigods are pitted against common enemies. It's a short but exciting read.
One great 'Percy Jackson Crossover Fanfic' is 'Percy Jackson and the Avengers'. It combines the world of Percy Jackson with the Marvel universe in a really interesting way. The characters interact in a believable manner and there are some really cool fight scenes.
Another possibility is that Percy somehow gets transported to Eragon's world. He has to adapt to the new environment and figure out how his demigod powers work there. Eragon could initially be suspicious of Percy but then they realize they can help each other. Percy could teach Eragon about water magic, which is new in Eragon's world, and Eragon could show Percy how to ride a dragon, which would be an amazing experience for Percy.
In a crossover fanfiction, the demon could be a result of some dark magic experiment gone wrong that combines the elements of both universes. For example, a sorcerer in the Percy Jackson world tries to use a spell from the Book of the Damned (from Supernatural) and accidentally creates a super - powerful demon. Percy and his friends, along with the Supernatural hunters, would then have to figure out how to stop it. This would involve the demigods using their unique powers like controlling water or flying, while the hunters use their knowledge of exorcisms and demon lore.
Another idea is that Peter discovers the existence of demigods while investigating a series of strange disappearances in Central Park. He stumbles upon Percy who is on a quest. They initially have some misunderstandings as they come from such different worlds, but then they figure out that they can help each other. Percy helps Peter understand the magical side of things, and Peter helps Percy with his knowledge of the city's layout and technology.
First, know both universes well. For a 'Percy Jackson Crossover Fanfic', you need to be familiar with the Percy Jackson world, like the gods, demigods, and Camp Half - Blood. Also, understand the other universe you're crossing it with. This knowledge will help you create believable interactions between characters.
One great place to start is Archive of Our Own (AO3). It has a vast collection of Percy Jackson crossover fanfics. You can search for crossovers with other popular series like Harry Potter or the Avengers. Just type in 'Percy Jackson crossover' in the search bar and you'll get a ton of results.