Wonder Woman would be an excellent addition. She has the strength and wisdom to deal with both Batman and Superman. She could be the voice of reason, trying to get them to stop fighting. Also, her own backstory and powers could be intertwined with the plot. For example, she might have some ancient knowledge about a threat that requires Batman and Superman to work together, and she has to convince them of this while also dealing with their egos and differences.
Batman would be the most interesting. He doesn't have superpowers like the Avengers, but he's still a formidable hero. His presence in their world would be like a wild card. He'd be constantly analyzing the Avengers and their enemies, and his dark, brooding nature would contrast with the more flashy and super - powered Avengers.
Another great pairing would be Superman and Captain America. Superman is an alien with god - like powers, while Captain America is a human with peak physical and moral strength. Cap could teach Superman about the value of human tenacity and leadership on a more down - to - earth level. And Superman could show Cap what true superhuman power looks like. They could work together to inspire the rest of the Avengers and any other heroes they encounter in a battle.
Definitely Superman and Thor. They both have super strength and are associated with powerful, other - worldly elements. Thor has his hammer and lightning powers, while Superman has his super - strength, heat vision, etc. It would be interesting to see them compete in a friendly strength - based challenge or fight side by side against a really strong foe.
Darkseid is another option. His power and his desire to conquer Earth could bring Batman and Superman together. He could target both Metropolis and Gotham, and his presence would require the two heroes to combine their skills. Batman's strategic mind and Superman's brute strength would be needed to face this powerful foe.
One idea could be that a powerful new villain emerges who has the ability to manipulate both Batman and Superman's minds. This forces them to fight against each other while the real enemy is pulling the strings. Another could be a situation where Gotham and Metropolis are in a territorial dispute, and Batman and Superman initially take sides based on their cities, but then realize they've been played.
Definitely Superman and Luke Skywalker. Luke is all about the Force and becoming a Jedi, while Superman has his own set of powers. They could learn from each other. Luke could teach Superman about the spiritual side of power, and Superman could show Luke how to use physical strength in new ways.
The Devil from Cuphead could be really interesting. Imagine him showing up in Bendy's world. His menacing presence and powers would be a huge threat. Bendy and his friends would have to figure out how to deal with this new and powerful foe. And the Devil could also be interested in Bendy's world for some dark purpose, like trying to corrupt it further.
Brainiac could also work well. He is an android with an insatiable thirst for knowledge and a penchant for collecting and destroying planets. In a crossover, he could target Earth, specifically Gotham and Metropolis. His advanced technology would pose a major challenge to both Superman and Batman. Superman's super - powers would be put to the test against Brainiac's powerful defenses, and Batman would need to use his wits to find a weakness in Brainiac's systems, leading to an exciting and complex story.
The Reverse - Flash would be really interesting. He could target both Batman and the Flash. For the Flash, he's a long - time nemesis, but for Batman, he'd be a new and extremely dangerous threat. His ability to manipulate the speed force and time could put Gotham in chaos in ways Batman has never seen before. And he could use his knowledge of the Flash to try and set traps for both heroes.
Another interesting pairing could be Batman and Daisy Johnson. Daisy has her inhuman powers, especially her seismic abilities. Batman could be intrigued by her powers and try to find ways to use them effectively in combat. And Daisy could learn a lot from Batman's combat training and his no - nonsense attitude towards fighting crime. They could form a strong duo when it comes to facing enemies that require both brute force and strategic thinking.