In a 'Game of Thrones' and 'Sherlock' crossover, Sherlock's deductive skills could be used to solve the mysteries in Westeros. He could figure out who really poisoned Joffrey or find out the secrets of the Faceless Men. It would be interesting to see how his logical mind would interact with the more superstitious and political world of 'Game of Thrones'.
In 'Game of Thrones Crossover Fanfiction', a cool concept would be crossing it with 'Alice in Wonderland'. Alice could wander into Westeros and disrupt the power balance with her strange and magical ways. Another idea is to cross it with 'The Hunger Games'. Have the districts be like the different regions of Westeros and the Capitol be King's Landing. And a crossover with 'Supernatural' where the Winchester brothers hunt down the supernatural threats in Westeros.
Well, for a 'a game of thrones crossover fanfiction', a crossover with 'Star Wars' would be cool. Picture the Nights Watch using lightsabers to fight the White Walkers. Or a crossover with 'The Matrix'. What if characters from Game of Thrones were trapped in the Matrix? Also, a crossover with 'Sherlock Holmes'. The detective skills of Sherlock could be used to solve the mysteries in Westeros.
A possible fanfiction could involve the creation of a new magic system in Westeros that combines the dark and mysterious nature of the Rinnegan with the existing magic in 'Game of Thrones'. For example, the White Walkers could be somehow related to the Rinnegan powers. Maybe the Night King was once a normal man who was experimented on with Rinnegan - inspired magic, which turned him into the powerful and terrifying being he is now. This would add a whole new layer of mystery and danger to the fight against the White Walkers.
In a Halo - Game of Thrones crossover fanfiction, the Forerunners' technology could be a huge factor. What if some of the Forerunner artifacts ended up in Westeros? Different houses might try to claim them, thinking they hold great power. The characters in Game of Thrones would be in awe of the advanced technology, and there could be a race to unlock the secrets of these artifacts, all while the political drama and power plays of Westeros continue.
One idea could be a scenario where the Vikings' raiding parties encounter the Night's Watch from Game of Thrones. Maybe they initially see each other as threats, but then realize they could be useful allies against the White Walkers. Another could be a story about a character from Vikings, like Ragnar Lothbrok, being magically transported to Westeros and having to navigate the complex politics there, similar to how he did in his own land.
One idea could be a character from 'Dishonored' getting transported to the world of 'Game of Thrones'. Maybe Corvo could use his powers to navigate the dangerous political landscape of Westeros. He could use his blink ability to quickly move through the Red Keep, unseen by guards, and gather information that could change the balance of power among the houses.
A unique idea could be Smaug being tamed by Bran using his warging abilities. Bran, with his connection to animals and his growing powers, might be able to reach out to Smaug's mind and form a bond. This would completely change the role Smaug plays in the 'Game of Thrones' universe.
Another plot could involve the Prince of Darkness being a key figure in a prophecy that the maesters have long ignored. As he emerges, he begins to gather followers who believe he is the answer to the chaos in Westeros. His actions could lead to a split between those who follow the traditional religions of the land and those who are drawn to his dark allure.
Another plot could involve a White Walker invasion in Skyrim. The Night King could lead his army through a magical portal that connects the two worlds. The people of Skyrim, including the various guilds, would have to team up with the houses of Westeros to fight this common enemy. The mages of Skyrim could share their knowledge of magic with the Red Priests and vice versa.
Well, for a 'Game of Thrones Crossover Fanfic', a cool concept would be to cross it with 'Narnia'. The Starks could find themselves in Narnia and have to deal with the White Witch. Also, crossing it with 'The Hunger Games' would be interesting. Picture the different houses competing in the Hunger Games - style battles. And how about a crossover with 'Sherlock Holmes'? Sherlock could solve the mysteries in King's Landing.