I think Luke Skywalker and Carlisle Cullen would be great characters to cross over. Luke, with his strong connection to the Force, could sense the different nature of Carlisle, a 'good' vampire. They could have discussions about morality and power. And then there's Leia. She's a strong - willed leader, and in a crossover, she could face off against the Volturi, trying to bring some sort of order or justice to the vampire world in the Twilight - Star Wars mash - up.
Edward from Twilight could be a likely candidate. His brooding nature and special abilities might make for an interesting interaction with the Jedi or Sith in Star Wars. He could either be seen as a potential threat or an ally. Another would be Ahsoka Tano from Star Wars. Her strong will and combat skills could be interesting when pitted against the vampires of Twilight.
For a Twilight - Star Wars crossover, Jacob Black could be an interesting character to cross over. His ability to transform into a wolf could be seen as a unique power in the Star Wars universe, perhaps like a new kind of alien species. And from Star Wars, Darth Vader. His dark and powerful presence would be a contrast to the vampires in Twilight. The vampires might either fear him or try to use his power for their own ends.
Han Solo and Commander Riker are also often crossed over. Han's roguish charm and piloting skills combined with Riker's military strategy and charisma make for an exciting pairing. They could be on a mission together, trading quips and sharing their different experiences from their respective universes. Another popular crossover is between Luke Skywalker and Spock. Luke's connection to the Force and his journey to become a Jedi, compared to Spock's logical Vulcan upbringing, offers a lot of room for character development and interesting interactions in fanfiction.
Yoda and Alfred could also have an interaction. Yoda is a wise Jedi master, and Alfred is Batman's wise and loyal butler. They could exchange wisdom and perhaps Yoda could give Alfred some insights about the Force that Alfred could then use to help Batman in some way.
Loki and Draco Malfoy would be a likely crossover. Loki is the mischievous god in the MCU, and Draco is a bit of a troublemaker in the Harry Potter world. They could team up and cause all sorts of chaos. Maybe Loki would teach Draco some of his more devious tricks, and Draco could introduce Loki to the pure - blood ideology of the wizarding world, which could lead to some really interesting storylines.
Gibbs would be really interesting. His no - nonsense attitude and skills as an investigator in the NCIS world would contrast greatly with the more otherworldly characters in Twilight. He might not believe in vampires at first, but then be forced to accept it as he digs deeper into a case.
Well, Sabine Wren from Star Wars Rebels would be a great candidate. She has a strong connection to Mandalorian culture already. She could interact with Din Djarin from The Mandalorian. They could exchange stories about their experiences with Mandalorian traditions and perhaps even team up to fight against the Empire.
Buffy and Luke Skywalker could be an interesting pair. Buffy is a strong fighter and leader in her world, and Luke is a key figure in the Star Wars universe. They could learn from each other's combat styles and leadership skills.
Luke Skywalker and Marty McFly are often popular choices. Luke's heroism and Jedi powers combined with Marty's relatable and adventurous nature can make for great stories. Another popular combo is Darth Vader and Doc Brown. The contrast between the dark, powerful Sith Lord and the eccentric inventor can create a lot of drama and humor in a fanfiction.
I think Darth Vader and Dr. Doofenshmirtz would make an interesting crossover. Darth Vader's dark and menacing presence combined with Dr. Doofenshmirtz's comical evil - scientist shtick could lead to some really funny and unexpected interactions. Maybe Dr. Doofenshmirtz tries to steal Vader's lightsaber for one of his 'evil -inator' plans, and Vader is just completely confused by this strange little man.
Another likely crossover could be between Giorno Giovanna and Wolverine. Giorno's ability to create life with Gold Experience and Wolverine's healing factor and berserker rage are both very unique powers. They could have an interesting relationship, either as allies learning from each other's powers or as opponents in a battle of wills.
Definitely Harry Potter and Luke Skywalker. They both are heroes on a journey to defeat great evils. They could learn from each other's experiences and powers. Harry could show Luke some of the more subtle forms of magic, and Luke could teach Harry about the Force.