Well, a really cool plot could be that the Frozen world is actually a long - lost planet in the Star Wars galaxy. The characters from Frozen get involved in the Galactic Civil War. Maybe Kristoff, who is used to cold environments, helps the Rebel Alliance on an ice - covered planet. Elsa could also use her ice powers to create defenses against the Empire's attacks, like building ice walls around Rebel bases. And Anna could befriend some of the alien species in the Star Wars universe and convince them to join the fight against the Empire.
A really cool fanfiction idea would be if Kylo Ren somehow ended up in the world of Frozen. He could be initially seen as a threat, but then Elsa realizes that he has some good in him due to his internal conflict, much like her own struggle with her powers. Or perhaps a story where the Ewoks meet the trolls from Frozen. They could exchange their knowledge of the forest and magic respectively.
One interesting storyline could be Princess Leia and Elsa teaming up. Maybe they use their leadership skills and powers respectively to save both galaxies from a new threat that somehow spans across the Star Wars and Frozen universes. For example, a dark force that freezes planets in the Star Wars galaxy while also causing chaos in Arendelle.
One idea could be a crossover with the original Star Wars trilogy characters. For example, having Luke Skywalker meet the Rebels crew and learn from their guerilla warfare tactics against the Empire. It would be exciting to see how their different fighting styles blend and how they interact with each other.
One plot idea could be Superman being transported to the Star Wars universe. He might use his powers to help the Rebel Alliance. For example, his super strength could be used to move large objects during battles or his heat vision to take out enemy ships. Another idea is that he teams up with Jedi. He could learn about the Force and they could combine their powers to fight the Sith.
One idea could be Jedi coming to Earth to train a select group of humans with Force - like abilities. Another could be a Sith Lord arriving on Earth and causing chaos, and Earth's heroes have to team up with Star Wars characters to stop him. Maybe there's a discovery of a hidden Star Wars - related artifact on Earth that has the power to change the balance of the Force.
One idea could be that the Spartans from Halo are sent through a wormhole and end up in the Star Wars galaxy. They could then get involved in the Clone Wars, with their advanced technology and combat skills being a huge asset or a source of great confusion among the different factions. Maybe they team up with the Jedi at first, but then some misunderstandings occur due to their different ways of handling situations.
One plot idea could be Thrawn crossing over into an alternate Star Wars timeline where the Jedi Order never fell. He could find himself in a situation where he has to adapt to a galaxy full of powerful Jedi. Another idea is a crossover with a different sci - fi universe, like Star Trek. Thrawn might use his tactical genius to face off against the Federation. Or perhaps a crossover with a post - apocalyptic Star Wars setting, where Thrawn has to lead a group of survivors against new threats.
A great plot could be that Master Chief somehow gets transported to the Star Wars universe. He could find himself in the middle of a battle between the Sith and the Jedi. His combat skills and advanced armor would be a huge asset to either side. Or perhaps there could be a story where the Forerunners have some ancient connection to the Force in the Star Wars galaxy. This could lead to a search for lost Forerunner technology that could change the balance of power in the Star Wars universe.
One idea could be a group of Guardians from Destiny being transported to the Star Wars universe. They could team up with the Jedi to fight against the Sith and the Darkness that threatens both universes. Maybe they would introduce their advanced weaponry and abilities to the Star Wars characters.
Perhaps in a Star Wars Twilight crossover fanfiction, the Force could be seen as a kind of super - power in the Twilight universe. A Jedi could come to train the Twilight characters in how to use this 'new' power. They would have to adapt their Jedi teachings to fit the different nature of the Twilight world, which has its own set of rules regarding vampires and werewolves.