Well, a really cool concept for a Harry Potter Pokemon crossover fanfiction would be if the Triwizard Tournament tasks involved Pokemon instead of the usual magical challenges. For example, the first task could be to capture a wild and powerful Pokemon. Or perhaps the Dark Mark is actually related to some dark - type Pokemon that Voldemort has managed to control. And imagine if Harry had a Pikachu as his sidekick, using its electric attacks against the Dementors.
One idea could be that Hogwarts students discover Pokemon in the Forbidden Forest. They could start training them as part of a new magical - creature - handling class. Another idea is that a powerful Pokemon like Mewtwo ends up at Hogwarts and causes chaos among the students and teachers, who have to use their magic to deal with it. Also, a wizard could accidentally cast a spell on a Pokeball and create a new, hybrid Pokemon - magic creature.
One idea could be that Hogwarts students discover Pokemon in the Forbidden Forest. They could start training them and use their powers in magical duels. For example, Pikachu's electric attacks could be used against dark wizards. Another idea is that Pokemon could be used in the Triwizard Tournament tasks, adding a new and exciting element to the competition.
In 'Harry Potter x Pokemon fanfiction', an interesting concept could be the magical creatures in the Harry Potter universe interacting with Pokemon. For instance, the Hippogriffs could befriend Flying - type Pokemon, and the Centaurs could have some sort of relationship with Grass - type Pokemon. Also, the spells in Harry Potter could have an impact on Pokemon. Maybe the Stupefy spell could temporarily paralyze a Pokemon, and the Protego spell could protect against a Pokemon's attack. This would create a whole new dynamic between the two universes, and characters from both worlds would have to adapt to these new interactions.
One idea could be a crossover with the Harry Potter universe. Pokémon could be integrated into Hogwarts, like having Pikachu as a familiar for a wizard. Another could be a crossover with the world of Final Fantasy. Pokémon trainers could team up with Final Fantasy characters to battle a common enemy. A third idea is a crossover with the Marvel universe, where Pokémon might have unique powers when exposed to the Infinity Stones.
Perhaps there could be a magical object in 'Harry Potter' that is somehow related to the werewolves in 'The Howling'. For example, a spell book that has the secrets to controlling werewolf transformations. The characters from both worlds could be on a quest to find this book and in the process, they learn more about each other's worlds and how magic works differently in each.
A great idea for 'harry potter and friends crossover fanfiction' is a crossover with 'Narnia'. The magical world of Narnia and Hogwarts have some similarities. Harry and his friends could enter Narnia through a magical portal in Hogwarts. They could help the Pevensie children in their battles against the White Witch. Another option is a crossover with 'The Chronicles of Prydain'. Harry and his friends could journey to Prydain and encounter the magical creatures and challenges there. And a crossover with 'Fantastic Beasts' but in a different way, like the main characters from 'Harry Potter' meet Newt's ancestors and have adventures with them.
Maybe in this fanfiction, the Death Eaters are somehow connected to an evil ninja clan in the Naruto universe. Harry and Naruto then have to team up to fight against this combined threat. Naruto could teach Harry how to use chakra to enhance his physical abilities, and Harry could show Naruto some of the more subtle uses of magic, like invisibility spells that could be useful for stealth missions.
Maybe a Witcher potion - making concept could be introduced to the Hogwarts potions class. For example, a character from Harry Potter, like Hermione, could be intrigued by the complex and powerful Witcher potions. She might try to study them and combine them with her own magical knowledge. This could lead to new discoveries in both magical systems.
Another idea is to have the Death Eaters somehow get access to Hollow powers. This would create a whole new level of threat in the Harry Potter universe. The characters from Bleach could then be called in to help the Order of the Phoenix deal with this new threat. Harry Potter might learn some skills from Ichigo about combat and vice versa.
Another interesting concept is a character from Harry Potter, like Harry himself, ending up in Forks. He could discover the existence of vampires and werewolves there. He might try to use his magic secretly while also being fascinated by the different supernatural rules in that world. He could even form an unlikely friendship with Bella or Edward, sharing his knowledge of magic with them.
One idea could be a crossover with the Lord of the Rings universe. Harry and his friends could find themselves in Middle - earth, having to deal with Sauron's forces while also using their magic. Another could be a crossover with the Star Wars galaxy, where wizards and witches interact with Jedi and Sith. Maybe they could learn from each other's use of the Force and magic.