Well, one possibility could be that Godzilla somehow ends up in the wizarding world. Maybe a powerful dark magic spell goes wrong and creates a portal that sucks Godzilla in. Harry and his friends at first think it's a new kind of dark creature created by Voldemort. They try to fight it using spells, but soon realize that Godzilla is not exactly evil. Godzilla might then start causing destruction in Hogwarts, and the wizards have to figure out a way to either send it back or control it without killing it.
In a 'Harry Potter and Godzilla crossover fanfiction', it could be that there is a magical item in the wizarding world that has the power to summon a great beast, and that item falls into the wrong hands. Godzilla is summoned and starts to make its way towards Hogwarts. Harry, Ron, and Hermione set out on a quest to find the source of the summoning and stop it. Along the way, they encounter various magical creatures that are also affected by Godzilla's presence. They also have to deal with the Ministry of Magic, which is in a panic and wants to use extreme measures to get rid of Godzilla.
Perhaps Godzilla is a creation of an ancient wizard who was experimenting with extremely powerful magic. This wizard was long forgotten, but with the resurgence of dark magic in Harry Potter's time, Godzilla is awakened. The Hogwarts professors study Godzilla to see if they can use their magic to communicate with it. Hermione might be the one to find some old scrolls that hint at how to deal with such a huge and powerful being. Meanwhile, Godzilla is just stomping around, not really understanding this strange new world of wizards.
A possible plot could be that Godzilla is accidentally teleported into the Pokemon world. The Pokemon trainers think he is a new, extremely powerful and dangerous 'Pokemon'. So they try to stop him. But as they try to fight Godzilla, they realize that their normal attacks have little to no effect. Then, a group of legendary Pokemon, such as Arceus and Lugia, decide to communicate with Godzilla. They find out that Godzilla is just as confused as they are about this new world. Together, they try to find a way to send Godzilla back to his own world while also dealing with the chaos that his presence has caused in the Pokemon world, like disrupted ecosystems and panicked Pokemon.
A plot could involve a mad scientist in the RWBY world who tries to recreate the power of Godzilla using Dust. However, the experiment goes wrong and starts to attract the real Godzilla. The RWBY teams then have to deal with the chaos caused by the approaching Godzilla. They might think that Godzilla is there to destroy their world, but as they fight, they discover that Godzilla is actually attracted to the unstable energy that the mad scientist created, which is also a threat to the balance of their world. So, they have to find a way to work with Godzilla to neutralize the dangerous energy source.
A plot could involve a mad scientist in the Marvel universe who, in an attempt to create a super - weapon, accidentally opens a portal to Godzilla's world. Godzilla comes through the portal and starts rampaging. The Fantastic Four, being experts in strange phenomena, are the first to investigate. Reed Richards tries to figure out a way to send Godzilla back while also protecting the city from its destruction. Meanwhile, the X - Men get involved as some mutants start to have strange reactions to Godzilla's presence. For example, Beast might be fascinated by Godzilla's unique physiology and try to communicate with it. Eventually, they discover that Godzilla is actually chasing a powerful energy source that the mad scientist's experiment also attracted. They work together to lead Godzilla to the energy source, which is then used to power a device that sends Godzilla back home.
One possible plot could be that Godzilla emerges in the Naruto world during a time of great unrest. The shinobi are initially terrified but Naruto, with his never - give - up attitude, decides to try and communicate with Godzilla. Maybe Godzilla is there because it senses a great evil in the Naruto world that is similar to the threats it has faced in its own. Naruto and his friends then have to figure out a way to work with Godzilla to defeat this common enemy.
In a Harry Potter and Superman crossover fanfiction, perhaps Voldemort discovers Superman's existence and tries to use his powers for his own evil deeds. He might try to control Superman's mind. But Superman, being the strong - willed hero he is, resists. Harry and his friends then team up with Superman to fight Voldemort. They learn a lot from each other. Harry learns about physical strength beyond magic, and Superman gets to understand the complexity of magic.
One possible plot is that a dark magic from the Darksiders universe seeps into the Harry Potter world. Harry and his friends discover that the only way to stop it is to learn some secrets from the Darksiders. So they embark on a journey through both worlds, meeting various characters from each along the way and using a combination of magic and the powers of the Darksiders to combat the threat.
The plot could involve Maleficent's magic interfering with Hogwarts' protective spells. She might be on a quest to find a powerful magical artifact hidden in Hogwarts that she believes will make her even more powerful. Harry and his friends suspect her motives and start to investigate. In the process, they learn about Maleficent's past and find some similarities between her story and their own fight against the dark forces in their world.
Well, it could be that Supergirl lands in the wizarding world somehow. Maybe she's chasing a bad guy who uses magic to escape to Hogwarts. And then she teams up with Harry Potter to fight the bad guy. Harry could teach her about magic while she teaches him about her superpowers.
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.
One possible plot could be that Moana's island is threatened by dark magic from the Harry Potter universe. Harry, Hermione, and Ron could be transported to Moana's world while on a mission to stop the spread of this dark magic. They would team up with Moana to use her knowledge of the ocean and the island's magic, along with their own wizarding skills, to fight off the dark forces. Maybe they'd have to face off against a wizard who has enchanted some of the sea monsters in Moana's world.