Well, perhaps Iron Man accidentally travels through a portal and ends up at Hogwarts. He could be mistaken for a new kind of magical creature at first. Then he teams up with Harry Potter. Iron Man starts to teach the students about Muggle technology and in return, Harry shows him the wonders of magic. When a group of Death Eaters try to steal Iron Man's suit to use it for evil purposes, Harry and Iron Man join forces to defeat them.
One possible plot could be that Iron Man's technology somehow gets transported to the wizarding world. Harry Potter and his friends are intrigued by this strange new technology. Iron Man, on the other hand, is baffled by magic. They have to work together to stop a threat that combines dark magic and advanced technology. Maybe Voldemort gets his hands on some Stark Industries weapons and they need Iron Man's expertise to disarm them while Harry uses magic to counter Voldemort's spells.
Well, the plot might be that in a parallel universe, Harry Potter grows up with a love for both magic and technology. He idolizes Iron Man and decides to create his own version of Iron Man - like tech using magic. This causes a stir in the wizarding world as it challenges the traditional ways. Meanwhile, the muggles start to notice strange magical - technological phenomena. Harry has to deal with the opposition from the wizarding establishment while also protecting his new inventions from falling into the wrong hands, all while being inspired by Iron Man's innovation and heroism.
A plot could involve Slender Man corrupting some of the magical creatures in the Harry Potter universe. For example, he could turn some of the centaurs or thestrals into his minions. Harry and Hermione would start researching about this strange new entity in the library. Ron, on the other hand, would be more skeptical at first. But as the situation worsens, they all team up. They might seek help from Hagrid who has knowledge of the more unusual creatures and together figure out a way to stop Slender Man from spreading his influence further.
A cool plot could be that the people of Westeros mistake Iron Man for some kind of powerful sorcerer because of his high - tech suit. The Lannisters might try to recruit him for their own gain. But Iron Man, being the hero he is, would see through their schemes. He could then start his own quest to find a way back home while also getting involved in the fight against the various threats in the Game of Thrones world. He might end up using the resources in Westeros to upgrade his suit in unique ways, like using Valyrian steel in its construction.
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.