Well, a great concept for an Arrow - Avengers crossover fanfiction would be a race against time. A powerful and evil force is about to destroy both universes. The Avengers and Arrow team have to work together. Black Widow and Speedy could team up and use their acrobatic and combat skills to infiltrate the enemy's base. Thor could help Oliver with his new - found knowledge of magic arrows. And the Hulk could be the brute force that the Arrow team sometimes lacks in their battles against meta - humans.
One idea could be that Oliver Queen gets transported to the Avengers' universe. He could teach them some of his stealth and archery skills. Maybe he helps Hawkeye improve his arrow techniques. Another idea is that the Avengers come to Star City. They help Oliver fight a new, super - powered villain that is too much for him to handle alone. The Avengers' powers and teamwork could combine with Arrow's street - level fighting style in an interesting way.
One idea could be that Oliver Queen from Arrow gets transported to the Avengers' universe. He could teach them some of his unique archery skills and in return, the Avengers could show him advanced technology like Stark's Iron Man suits. Maybe they team up to fight a common enemy that has the ability to manipulate time, causing chaos in both their worlds.
One possible plot could be that Oliver Queen gets transported to the Avengers' universe. He teams up with Hawkeye, sharing their archery skills and combat tactics. They could go on a mission to stop a new threat that combines the technology of the Arrowverse and the super - powered enemies of the Avengers.
One idea could be to explore a world where the characters from 'Lucifer' and 'Arrow' are forced to team up to stop a common supernatural threat that is beyond the capabilities of either group alone. For example, a powerful demon that is using advanced technology to cause chaos in both their worlds.
One idea could be Batman coming to Star City to help Arrow deal with a new, extremely dangerous criminal organization that has ties to Gotham. This could lead to some great fight scenes as they combine their skills and resources.
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.
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.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3) or FanFiction.net. These sites have a large collection of fanfictions. Just search for 'Arrow and Avengers crossover' and you'll get a list of relevant stories. Some might be really good, while others may not be to your taste. It's all about exploring and finding the ones that resonate with you.
A great plot could involve the two heroes swapping cities for a while. Arrow tries to deal with Gotham's crime underworld while Batman goes to Starling City to investigate a series of strange disappearances that might be linked to a powerful criminal organization there. This would lead to both heroes having to adapt to different environments and crime - fighting styles.
Perhaps there could be a story where Lex Luthor somehow gets hold of some of Arrow's technology and Clark has to work with Oliver to retrieve it. They would have to combine their skills, Clark's superpowers and Oliver's archery and combat expertise.
Maybe there could be a crossover where the Flash accidentally travels to the Arrow's universe and they have to work together to get him back to his own world. Along the way, they discover a common enemy that has been operating in both universes.