A plot could be centered around Obito's past and how it parallels some of the characters in Harry Potter. For example, Obito's experience of loss and his turn to the dark side could be compared to Severus Snape's story. Obito could be drawn into the conflict between the Order of the Phoenix and the Death Eaters because of his own complex moral compass. He could use his knowledge of different jutsu to create new spells or counter - spells in the wizarding world, all while exploring his own redemption arc similar to some of the characters in Harry Potter.
A possible plot could be that in a parallel dimension, Harry Potter is actually Obito Uchiha reincarnated. He is born into the wizarding world but still has some latent memories and powers from his past life as Obito. As he grows up in Hogwarts, he discovers his unique abilities which are a blend of magic and the powers of the Sharingan. He uses these to uncover a hidden conspiracy within the wizarding world that is related to an ancient dark magic that has similarities to the dark powers in Obito's original world. Along the way, he has to deal with his own inner demons, just like Obito did, and also face off against the traditional threats in the Harry Potter universe like Voldemort and his followers, but with a whole new set of skills and a different perspective due to his dual - natured identity.
Well, perhaps the magical creatures from the Harry Potter universe end up in the '300' setting. Dragons could be used by the Spartans to fight their enemies. The centaurs could also join the battle, lending their archery skills. And Harry could learn some combat skills from the Spartans, which he could then use back in the wizarding world to fight Voldemort's Death Eaters.
The Stargate could be a portal between different magical realms in the Harry Potter universe. For example, it could lead to a place where ancient and more powerful magic exists. Wizards from different schools around the world could team up with Stargate explorers to uncover the secrets of this new place. There might be a new threat emerging from this realm that requires both magic and Stargate technology to defeat. This would bring together characters like Harry Potter and Jack O'Neill to lead the charge against the common enemy.
Well, perhaps there's a rift in the multiverse that connects Central City to Hogwarts. The Flash, while chasing a villain, gets sucked into the wizarding world. Harry Potter and his friends initially suspect him as a threat but then realize his good intentions. They then combine their powers - the Flash's speed and the magic of the wizards - to fight a common enemy. For example, the Flash could use his speed to distribute protective spells all over Hogwarts really quickly, while Harry and his friends focus on the offensive magic against the bad guys.
One idea could be that Carly and her friends discover a magical portal in their apartment that leads to Hogwarts. They then have to navigate the wizarding world, with Carly being fascinated by all the magic. Meanwhile, Harry Potter and his friends are intrigued by the strange Muggle - like devices the iCarly gang has. They end up teaming up to solve a mystery that involves both the wizarding and Muggle worlds.
Well, perhaps the Death Note from the Bleach universe gets mixed up with the magic in Harry Potter's world. A powerful wizard could get hold of it and start using it in ways that disrupt the balance of life and death in both worlds. Harry and his friends would have to figure out how to stop this misuse, with the help of some Bleach characters who understand the true nature of the Death Note.
One idea could be that Eragon, while on one of his adventures in Alagaësia, accidentally creates a portal that leads him to Hogwarts. There, he meets Harry Potter and they quickly realize they have a lot in common. They could team up to fight against a dark force that somehow threatens both their worlds, like a new type of dark magic that combines the magic of Alagaësia and the dark arts from the wizarding world.
In a more comical plot, Hagrid could accidentally stumble upon a small Transformer while in the Forbidden Forest. Thinking it's a strange magical creature, he brings it back to Hogwarts. The Transformer, being a bit lost in this new magical world, causes all sorts of chaos in the castle. Harry and his friends have to figure out how to get the Transformer back to where it belongs while also dealing with the daily challenges at Hogwarts.
One possible plot could be that the Duel Monsters from Yu - Gi - Oh! are introduced to the wizarding world of Harry Potter. Wizards start using them in duels instead of their traditional spells. Harry and his friends have to learn the new rules of these duels and face off against a dark wizard who has mastered the most powerful Duel Monsters.
Well, perhaps Spyro discovers a magical portal in his world that leads to Hogwarts. Once there, he becomes a sort of mascot for Gryffindor because of his brave nature. The students try to learn from Spyro how to better communicate with magical beasts, as he has a special connection with them. Meanwhile, Voldemort or one of his followers might see Spyro as a threat and try to capture him. Harry and his friends then have to protect Spyro and in the process, learn more about Spyro's world and its magic.