One possible interesting plot could be a crossover where the heroes from the Throne of Heroes are summoned into the Harry Potter world. They could use their unique powers and abilities to help in the fight against Voldemort. For example, a heroic archer from the Throne of Heroes could provide long - range support during battles at Hogwarts.
In a 'Harry Potter Throne of Heroes fanfiction', an interesting plot could involve the Hogwarts founders as heroes in the Throne of Heroes. They are summoned back to the modern - day wizarding world, but they have lost some of their memories. Harry and his friends must help them regain their memories and use their ancient wisdom to solve a new, greater threat that is looming over the wizarding world.
Harry Potter himself could be the main character. He could be the one who discovers the connection between his world and the Throne of Heroes. He might then use this knowledge to gain new allies and powers to fight against the dark forces in his world.
One possible plot could be that Voldemort discovers a way to use dark magic to control the Elemental Heroes, and Harry has to learn how to properly summon and befriend them to fight back. He might start with the help of Hermione, who discovers an old, forgotten spell book in the library that has the secrets of summoning these heroes.
Perhaps the heroes assemble to save a powerful magical artifact that is being targeted by a group of dark forces. Each character could bring their own knowledge and abilities to the quest. For example, Hermione's vast knowledge of spells and potions would be crucial, while Harry's courage and experience in facing dark wizards would lead the group. They might also encounter new magical creatures along the way that they have to either befriend or fight.
One idea could be that Mewtwo somehow gets transported to the Harry Potter universe. It could be mistaken for a very powerful magical creature. Harry and his friends could initially be wary of it, but then realize it has no intention of harm and they team up to fight against the dark forces in the wizarding world using Mewtwo's psychic powers.
Another plot could be that Voldemort discovers Powergirl's existence and sees her as a threat. He tries to manipulate the wizarding world against her. But Harry and his friends believe in her and together they work to expose Voldemort's lies and also learn from Powergirl about different ways of fighting evil. Powergirl could introduce new concepts of justice and heroism to the wizarding world.
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.