He might fit in as a sort of mentor figure. He has years of experience fighting crime in Gotham. He could teach the younger Avengers like Spider - Man (if he's in the mix) some valuable lessons about perseverance and the importance of a strong moral code. Also, his physical combat skills would be useful in hand - to - hand battles against powerful foes.
Batman would fit in by being the ultimate strategist. The Avengers sometimes jump into action without a fully thought - out plan. Batman's meticulous planning would force them to be more organized. He could also provide a more grounded perspective. Many of the Avengers have superpowers and deal with large - scale threats from outer space or magic realms. Batman, coming from the streets of Gotham, would remind them of the importance of protecting the everyday people.
Harry could fit in by using his magic for reconnaissance. His invisibility cloak would be great for spying on enemies unnoticed. The Avengers could use this to their advantage when planning attacks.
Maybe in the fanfic, Batman's rogues gallery somehow teams up with some of the Avengers' villains. This forces Batman and the Avengers to work together. Batman could introduce his unique gadgets and combat style to the Avengers, while they could show him their superpowers up close. For example, Iron Man could be intrigued by Batman's utility belt and try to create his own version of some of the gadgets.
He could fit as a powerful ally. His mastery over death gives him abilities that could enhance the Avengers' capabilities.
He could be a great addition for his brute strength. Just imagine him in a battle against a powerful enemy like Thanos. He could hold his own and even distract Thanos long enough for the other Avengers to come up with a strategy.
In a fanfic, Harry Potter could enter the Avengers' story through a magical portal. Once there, he could use his magic to complement the Avengers' skills. For example, his ability to communicate with snakes could be useful if they encounter snake - like villains. His experience with horcruxes might also give him insights into dealing with powerful and hard - to - destroy enemies in the Avengers' world. His wand could be a unique weapon in their battles, and his ability to perform complex spells could turn the tide in difficult situations.
It could be really exciting. Batman's detective skills and gadgets would add a new dimension to the Avengers. He might outwit some of the Avengers' enemies with his superior intellect. For example, when facing Loki, Batman could use his knowledge of psychology to manipulate Loki's actions. His utility belt with all its cool gadgets like the grappling hook and batarangs would be a great addition to the team's arsenal.
Nico would fit in by bringing his unique powers. His ability to control the dead could be a huge asset in battles. For example, he could raise an army of skeletons to fight alongside the Avengers. His shadow - traveling would also be great for quick getaways or surprise attacks.
One possible plot could be that Batman's Gotham is threatened by a powerful villain who has some connection to the Avengers' universe. Maybe Loki decides to cause chaos in Gotham as part of a larger plan against Earth. Batman, being the detective he is, starts to investigate and soon realizes that this is no ordinary criminal. He then somehow gets in touch with the Avengers, perhaps through SHIELD's intelligence network. Together, they combine their skills and resources to take on Loki and his minions. Batman's stealth and strategic mind would complement the Avengers' superpowers.
Well, it could be really chaotic. The Avengers come from their own universe with superpowers and complex relationships. A Batman fanfic usually has its own dark and gritty tone. If they met within the context of a fanfic, there might be a clash of ideologies. The Avengers might not understand Batman's more brooding and solo nature, while Batman fans might find the Avengers' flashy powers a bit over - the - top. Maybe the Avengers would try to recruit Batman from the fanfic world, thinking his detective skills could be useful.