Ares could also be a good choice. He wants to spread war and chaos. He could manipulate events in Gotham to start a huge conflict. Batman, being the protector of Gotham, and Wonder Woman, who opposes Ares' war - mongering ways, would have to join forces to stop him. Ares could use his powers to create illusions and turn the citizens of Gotham against each other, which would be a big challenge for our heroes to overcome.
Cheetah could be a great villain. She has a connection to Wonder Woman already, but in a crossover, she could be working with some of Batman's rogues like the Penguin. The Penguin could provide the resources while Cheetah does the dirty work in combat against Batman and Wonder Woman.
Lex Luthor. He is a brilliant and power - hungry villain. He could see the potential of teaming up with some of Wonder Woman's enemies to take down both her and Batman. He might try to create a super - weapon using technology and magic combined, which he believes can defeat them. Batman and Wonder Woman would need to use all their skills and resources to outwit Luthor.
Lex Luthor could be a great villain. He could be jealous of the relationship between Superman and Wonder Woman and create a plan to turn them against each other. He might use his intellect to create weapons that can target their weaknesses.
Lex Luthor could be a great villain. He could be after some technology in Spiderman's world that he wants to use to enhance his power in his own battles against Superman. At the same time, he might see Wonder Woman as a threat to his plans of world domination. He could use his intelligence to create complex traps and weapons. His corporate power would also allow him to manipulate situations in both the worlds of Spiderman and Wonder Woman.
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.
Athanatos could be a great villain. He's a powerful and immortal being who has been sealed away for centuries. But with the disruption of ancient magic (maybe caused by Lara's latest adventure), he is freed. He wants to conquer both the mortal and the Amazonian worlds. Lara's knowledge of archaeology and Wonder Woman's combat skills would be put to the test against his dark magic.
Lex Luthor could be an interesting antagonist in this scenario. He could be using his intelligence and resources to create a weapon that could neutralize both Batman and Wonder Woman. He might be working with some of Batman's rogues gallery or even some of Wonder Woman's enemies. His presence would add a different dynamic as he's a human villain but with extraordinary cunning and resources.
The Joker could be a great main villain. He could infiltrate the school disguised as a new student or a janitor. He starts causing chaos by spreading his brand of insanity among the students, like setting up pranks that turn dangerous. Batman would immediately recognize his presence, but the Joker is always one step ahead in causing mayhem. Wonder Woman would have to use her lasso of truth to try and get information from the students who have been influenced by the Joker.
Circe could be a great villain. She has powerful magic and could create all sorts of illusions and obstacles for Wonder Woman and Hawkgirl. She might try to turn them against each other or use their powers for her own dark purposes.
Lex Luthor would be a great choice. He could be causing trouble in Gotham as well as Metropolis. His intelligence and resources would pose a significant threat to both Supergirl and Batman. He might be trying to manipulate events to make the two heroes fight each other so he can carry out his evil plans.
At first, it might be a bit rocky. Batman is used to working alone and being in control, and Wonder Woman is a powerful and independent hero. But as they face challenges together, they would start to respect each other's abilities. They could develop a friendship based on mutual admiration for their different skills.
After the proposal, their relationship would likely become more public. They would no longer be just comrades in arms but an engaged couple. Their interactions would be more affectionate and they would start planning a future together.