One idea could be that Oliver Queen somehow gets transported to Westeros. He could use his archery skills to survive in the dangerous world. Maybe he'd join a faction, like the Night's Watch, and teach them his modern combat techniques.
A great plot idea for an Arrow - Game of Thrones fanfiction crossover would involve the magic in Game of Thrones. What if a magical object from Westeros made its way to Starling City? Oliver and his team would be baffled by this new element. They might have to seek help from someone who has knowledge of both worlds, like a character who has also traveled between the two, to deal with the consequences of this magical intrusion.
Definitely Jon Snow. His leadership skills and sense of justice would fit well in the world of Arrow. He could team up with Oliver Queen and they could exchange ideas on leading their respective groups.
Well, for 'Game of Thrones crossovers fanfiction', a cool one would be to cross it with 'The Chronicles of Narnia'. Imagine Arya Stark finding her way into Narnia and becoming part of the fight against the White Witch. Also, a crossover with 'Sherlock Holmes'. The detective skills of Sherlock could be applied to solving the mysteries and political intrigues in Westeros. And a crossover with 'The Hunger Games', where the citizens of the Seven Kingdoms are forced to participate in a similar brutal game.
One idea could be exploring what would happen if a minor character like Gendry had been secretly trained in magic. He could use his newfound powers to unite the smallfolk against the warring nobles. Another plot could revolve around a female knight from the North who disguises herself as a man to fight in the wars, and along the way, she discovers secrets about the White Walkers that no one else knows. Or perhaps a fanfiction where Daenerys and Sansa form an alliance much earlier and together they reshape the power dynamics of Westeros.
A really cool 'Game of Thrones fanfiction' plot could involve the resurrection of some of the dead characters in a different way. For example, what if Ned Stark was brought back not as a vengeful wraith but as a wise advisor to a new king or queen? His honor and wisdom could shape the future of Westeros in a completely new direction. And it would be interesting to see how the other characters react to his return.
Perhaps a fanfiction where Daenerys Targaryen lands in Westeros earlier and forms an alliance with the Starks before the events of the main series. This would completely shift the political landscape and the fight for the Iron Throne. She could bring her dragons to help fight the White Walkers from the start.
One idea could be exploring what would happen if a minor character, like Gendry, had a more central role in the fight against the White Walkers. He could lead a group of common folk and prove that the power doesn't always lie with the nobles.
One interesting crossover could be the Avengers having to deal with the political intrigue of Westeros. For example, Iron Man might use his technology to try and outwit the various lords vying for the Iron Throne, much like he does with his corporate rivals. Another could be Thor interacting with the gods in the Game of Thrones universe, perhaps recognizing some similarities between their powers.
One interesting crossover could be a scenario where the powerful vampires from The Originals find themselves in the political intrigue of Westeros from Game of Thrones. Maybe they get involved in the power struggles between the different houses, using their vampiric abilities to gain an edge. For example, Klaus Mikaelson could try to manipulate Cersei Lannister for his own ends.
A really cool fanfiction idea could be that the ancient prophecies in both Eragon and Game of Thrones are somehow related. Characters from both stories start to realize that their fates are intertwined due to these prophecies. This could lead to a grand adventure where they have to work together to fulfill or prevent the prophecies from coming true. For instance, Daenerys Targaryen and Eragon could join forces, with their dragons, to face a great evil that has been foretold in both of their worlds' prophecies.
A great crossover idea in the fanfiction could be the magic systems. Imagine Daenerys Targaryen learning about the Signs that Geralt uses. Her dragons could be intrigued by the magic of The Witcher world, and perhaps they could interact in ways that are both unexpected and exciting. This could lead to new alliances or battles depending on how the story unfolds.