I think Hermione would be really interesting. She's so intelligent and resourceful in the 'Harry Potter' world. In a fanfiction with 'Legends of Tomorrow', she could use her vast knowledge of magic to help the Legends understand and deal with magical threats they encounter during their time - traveling adventures. She might be able to figure out how to combine magic with their technology in ways no one else could.
Ray Palmer is also interesting. His scientific knowledge from Arrow combined with his experiences in Legends of Tomorrow make him a unique character. You could write about how he uses his tech - savvy skills to help the combined team in a crossover. He could be the one to come up with a plan to defeat a powerful enemy using his shrinking technology or other inventions.
I think it would be really interesting to focus on Hermione. Her thirst for knowledge would make her eager to learn about the world of Eragon, especially the dragon - riding and the different types of magic. She could also bring her logical thinking and problem - solving skills to the table, which would be very useful in both worlds.
Harry himself would also be a great focus. His experience with facing dark wizards in his own world would be put to the test in the Forgotten Realms. He could have to learn new magic quickly to survive and also figure out how to use his existing powers in a world with different magical rules. His connection to Voldemort might also play an interesting role, like if Voldemort's influence somehow seeps into the Forgotten Realms.
Luna Lovegood would be an unexpected but fascinating choice. Her unique perspective and belief in all kinds of magical creatures could make her very open - minded about the vampires and werewolves in the Twilight world. She might see them as just another type of magical being and try to find common ground, which could lead to some really interesting interactions and storylines.
Hermione would be really interesting. She's so intelligent and studious. If she traveled back in time, she could use her knowledge of magic history and spells to make a big impact. For example, she might be able to help the Order of the Phoenix in new ways during the First Wizarding War or she could introduce some modern magical concepts to the wizards of the past.
Nico di Angelo would be an interesting choice. His dark and brooding nature along with his powers over the dead would be a contrast to the more light - hearted aspects of the Harry Potter world in some ways. He could introduce the wizards to the concept of the Underworld and the spirits. And his ability to shadow - travel could be used in some really creative ways, like getting the group in and out of dangerous situations quickly, whether it's in Hogwarts or in the magical areas related to Greek mythology.
Doctor Strange would be an interesting character to focus on in a Harry Potter MCU fanfiction. He already has knowledge of magic in the MCU, but it's a different kind of magic compared to that in Harry Potter. He could compare and contrast the two magics, and perhaps even learn new spells from the Harry Potter universe. His presence could also bridge the gap between the two universes in terms of magic.
Harry Potter himself would be very interesting. Imagine him in the world of the K Project, trying to understand their power systems while still having his own magic. He could be a bridge between the two worlds, using his Gryffindor courage to face the challenges in the K Project universe.
Hermione Granger and Spock would be really interesting. Hermione is known for her intelligence and knowledge. Spock is also highly intelligent and logical. They could have some really in - depth discussions about the differences between magic and science. Hermione could try to explain the principles of magic to Spock, and Spock could attempt to make Hermione understand the Vulcan way of thinking and the science behind the Enterprise's technology.
I think it would be really interesting to focus on Hermione. She's so intelligent and curious. In Middle - earth, she could study the different magic and lore there. She might be the one to figure out how to combine the magic of the two worlds. For example, she could try to find a way to use the magic of Middle - earth to defeat Voldemort or help the Fellowship in a different way.