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.
John Constantine from Legends of Tomorrow could be a fascinating character to focus on. His dark magic and complex personality could add a whole new layer to an Arrow and Legends crossover. He could be the one to uncover a hidden magical threat that the two teams have to face together, and his interactions with the more morally upright characters from Arrow would be full of tension and drama.
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.
The Flash (Barry Allen) could also be a great character to include. Since he has crossovers with both Arrow and Supergirl in the actual shows. His light - hearted nature and super - speed abilities could add a different dynamic to the story. He could act as a mediator between Oliver and Kara when they have differences. Also, villains like Lex Luthor could be really interesting to explore in this crossover. His brilliant mind and devious plans could pose a significant threat to both heroes and force them to work together in new ways.
Maybe there's a powerful magical artifact that has the ability to destroy both the Arrowverse and the timeline that the Legends protect. The two teams join forces to find this artifact before it falls into the wrong hands. They face numerous challenges and battles along the way, and some characters might have to make sacrifices to save the day.
Raphael could be really interesting. In the 2003 version, he is hot - tempered and tough. In the 2012 version, he also has a strong personality. Seeing how he reacts to his counterpart and how they might either clash or bond could be a great focus. Maybe they have a friendly rivalry as they compare their fighting skills.
Ross could be really interesting. Since he's an archaeologist, in a crossover with a show like 'Indiana Jones' (in a fanfiction sense), he could go on an adventure with Indiana Jones. Ross would bring his academic knowledge while Indy would have the practical experience. Their interactions would be filled with Ross trying to over - analyze everything and Indy just wanting to get the job done.
Chiaki Nanami could be an excellent choice. She is the Ultimate Gamer, so if you cross her with a digital or virtual world, there are so many possibilities. She could use her gaming skills to navigate through a new digital realm, like a Matrix - like world. Her calm and intelligent nature would also make her a great character to lead the group in a crossover situation. She could figure out the rules of the new world quickly and help the others adapt.
Green Arrow and Hawkeye would have an interesting dynamic. They both use bows and arrows, but their styles and personalities are different. Hawkeye might be more laid - back in some ways, while Green Arrow is often more brooding. Their exchanges about archery techniques and their roles as heroes in their respective teams could be really engaging. Also, Laurel Lance and Black Widow could have some intense interactions. Laurel has her own struggles with justice and revenge, and Black Widow could offer her different perspectives on handling those emotions in the world of heroism.
For an Arrow - Avengers crossover fanfiction, some really interesting character pairings could emerge. For instance, Malcolm Merlyn and Loki. Malcolm is a master manipulator and Loki is the God of Mischief. They could either team up to cause chaos or be in a constant battle of wits. Also, Cisco Ramon from The Flash (since he often crosses over with Arrow) and Bruce Banner. Cisco could be fascinated by Banner's scientific knowledge and Banner could be interested in Cisco's work on the multiverse. And of course, Quentin Lance and Nick Fury. Quentin, as a police detective, and Nick Fury, as the head of S.H.I.E.L.D., could share their insights on how to keep their respective cities and the world safe.
Definitely Oliver Queen and Jim Gordon. Oliver is used to operating in the shadows and taking justice into his own hands in Starling City, while Jim is a cop trying to uphold the law in the corrupt Gotham. Their different approaches to crime - fighting would make for some great interactions.
Definitely Clark Kent and Oliver Queen. They come from different worlds but share a sense of justice. Their interactions would be fascinating as they learn from each other's methods of fighting crime. Clark could show Oliver the power of his super - abilities, while Oliver could teach Clark some of his stealth and strategic skills.