Ra's al Ghul could also be a fascinating villain in this scenario. His long - term goals and his connection to the Lazarus Pits would be something that both Deadpool and Batman would have to grapple with. Deadpool might be more interested in the potential immortality aspect of the Lazarus Pits, while Batman would be focused on stopping Ra's al Ghul's plans for Gotham and the world. Ra's al Ghul would see Deadpool as an unpredictable element and Batman as his long - time nemesis, making for a complex and interesting conflict.
The Joker would be really interesting. Imagine Deadpool meeting the Joker. Deadpool would be both fascinated and repelled by the Joker's insanity. The Joker, on the other hand, would be intrigued by Deadpool's indestructibility and chaotic nature. It would create a really wild dynamic, with Batman caught in the middle trying to stop both of them from causing too much mayhem.
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.
Ra's al Ghul would be a great choice. He has ties to both the Arrow universe and Batman's world. He could be manipulating events in both Star City and Gotham, forcing Arrow and Batman to team up to stop his grand scheme. His immortality and vast resources would pose a huge challenge for them.
Ra's al Ghul would be a fascinating villain in a crossover. He has a global view of crime and destruction, and his Lazarus Pit gives him a certain immortality. His plans could involve both Hell's Kitchen and Gotham in some grand scheme. Daredevil would be out of his depth dealing with Ra's al Ghul's long - term, world - changing plans, and Batman would have to bring Daredevil up to speed while also trying to stop Ra's al Ghul's latest plot.
The Riddler could be very interesting. He could create complex riddles that not only test Batman's detective skills but also stump Spiderman. His maniacal love for puzzles could be a great contrast to the more straightforward villains that Spiderman usually faces.
The Joker would be really interesting. Imagine him getting his hands on some of Oscorp's dangerous technology. He could use it to create chaos in both Gotham and New York in ways that neither Batman nor Spiderman have seen before. His unpredictable nature would make it hard for the two heroes to anticipate his moves.
For a more unexpected villain, how about Lex Luthor? He could see Harley and Deadpool as threats to his plans in Gotham or wherever their story takes place. He would bring his high - tech resources and strategic mind to the table, which would be a different kind of challenge for Harley and Deadpool compared to the villains they usually face.
Ra's al Ghul could also be a main antagonist. He might see Deadpool as a wildcard that could disrupt his plans for Gotham and the world. Ra's al Ghul's long - term goals of achieving immortality and controlling the world would put him at odds with both Batman and Deadpool. Deadpool's immortality might be something Ra's al Ghul wants to study or use for his own purposes, and Batman would do anything to stop Ra's al Ghul's evil schemes.
In a more extreme scenario, Deadpool could end up in Arkham Asylum and think it's a new kind of S.H.I.E.L.D. facility. He'd start interacting with the inmates there, and Batman would have to step in to deal with the chaos Deadpool is causing. Deadpool would see Batman as this dark and brooding figure and keep trying to get him to lighten up.
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.
Deadpool, without a doubt. His crazy antics, fourth - wall - breaking, and unpredictable nature would add a whole new level of chaos to the already volatile Suicide Squad. He would constantly be making jokes, getting into fights with the other members just for the fun of it, and finding unique ways to solve problems that the more traditional Squad members wouldn't think of.