One possible plot could be that Elektra Natachios, with her skills in combat and stealth, is somehow transported to the Harry Potter universe. She could be mistaken for a new type of dark wizard at first. But then she teams up with Harry Potter to fight against a common enemy, perhaps a new dark force that combines the dark magic of the Potterverse with the more physical and political threats Elektra is used to. They learn from each other's skills, Harry teaching Elektra about magic and she teaching him some of her hand - to - hand combat and strategic thinking.
She could fit in as a powerful ally. Given her combat skills, she could be like a Muggle - born with extraordinary non - magical fighting abilities. She might join the Order of the Phoenix and use her skills to protect the wizarding world from the Death Eaters. For example, when there are battles in places like Hogsmeade or at Hogwarts, she could take on the Death Eaters in close - combat situations where magic might not be as effective, like in narrow alleyways or during hand - to - hand duels.
A plot could involve a time - travel scenario. Tywin Lannister is sent forward in time to the era of Harry Potter. He is shocked by the modern - day wizarding world. He tries to assert his authority but quickly realizes he is out of his depth. Harry Potter, being the good - natured hero, tries to help Tywin adjust. However, some of the darker elements in the wizarding world see Tywin as a potential tool to gain power and try to manipulate him, leading to a complex web of intrigue and adventure.
One possible plot could be that Harry Potter somehow travels to the Star Wars universe and meets Anakin Skywalker. They could team up to fight a common enemy, like a dark wizard who has also gained some sort of Sith - like powers. Harry could use his magic skills, and Anakin his Jedi abilities, and they'd learn from each other's strengths and weaknesses.
One possible plot could be that Harry discovers a hidden magical realm in the Pokémon world during one of his adventures. There, he meets Rayquaza. Rayquaza, being a powerful Pokémon, senses the strong magic within Harry. Together, they have to fight against a dark wizard who has found a way to corrupt Pokémon and use them for evil purposes in both the wizarding world and the Pokémon world.
Maybe the Timekeeper is actually a descendant of an ancient wizarding family who was tasked with keeping time in balance. In the fanfiction, Voldemort discovers this and tries to use the Timekeeper's powers to go back in time and prevent his own downfall. The Timekeeper has to fight against Voldemort's minions while also trying to find a way to protect the timelines. Harry and his friends get involved when they notice strange time - related disturbances around the school. They join forces with the Timekeeper to stop Voldemort's evil plan.
In a fanfiction, the Triforce could be split among Harry, Ron and Hermione. Harry gets the Triforce of Courage, Ron the Triforce of Power (which he learns to use in a more responsible way), and Hermione the Triforce of Wisdom. Together, they combine their powers of the Triforce with their magic skills to defeat Voldemort once and for all. The Triforce's power could also be used to reform the wizarding world, bringing more equality and peace.
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.
Perhaps in this 'Harry Potter in Vegas' fanfiction, Harry accidentally apparates to Vegas instead of his intended destination. There he meets a group of American wizards who are using Muggle Vegas as a cover for a secret magic convention. Harry gets involved in a mystery where a powerful magical artifact has gone missing and he has to find it before it falls into the wrong hands.
One possible plot could be that the Kubikiribocho, the sword in Naruto, somehow finds its way into the Harry Potter universe. Harry discovers it during one of his adventures in the Forbidden Forest. He initially has no idea how to use it but gradually realizes it has some unique powers that can be harnessed against Voldemort. For example, it might be able to cut through dark magic spells. However, there are also some negative aspects to the sword as it tries to corrupt Harry a bit, just like the influence of the Horcruxes. Harry has to fight against this internal battle while also using the sword's power to defeat Voldemort.
A possible plot is that Tigger, with his boundless energy, teams up with Harry Potter. Tigger's unique ability to bounce high and far could be useful in Quidditch. He might bounce on the brooms and make them go even faster, or he could bounce around the Quidditch pitch, distracting the opposing team. Meanwhile, Harry could teach Tigger about the wizarding world and its secrets.