Ares, the God of War from Wonder Woman's mythology. He could see the union of Superman and Wonder Woman as a threat to his plans of spreading chaos and war. He could use his godly powers to manipulate events and try to break them apart while also causing destruction on a large scale.
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.
Darkseid would also be a formidable foe. He might be interested in the power that Superman and Wonder Woman possess together. He could send his minions to test them first and then engage in a full - scale battle himself, using his Omega Beams and vast army to try and conquer Earth with Superman and Wonder Woman as the main obstacles in his way.
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.
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.
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.
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.
A powerful alien warlord could be the main villain. This warlord might have his eyes on Earth because of its resources or strategic location. Supergirl and Wonder Woman would have to use their unique powers and teamwork to defeat him. He could have an army of minions and advanced technology that makes him a formidable foe. They would need to figure out his weaknesses and come up with a plan to stop his invasion.
Well, it depends on the situation. If the fight takes place in the Naruto universe where Naruto can draw on natural chakra more easily and has the home - field advantage, he could be very strong. He also has his Nine - Tails chakra which is extremely powerful. On the other hand, Wonder Woman has years of combat training and her divine weapons. In a battle of wits and strategy, Naruto's experience in fighting various opponents in his world might give him an advantage, but Wonder Woman's overall power set is also very formidable.
Lex Luthor would be a great villain. He could be plotting to destroy Superman once and for all while also trying to outsmart Batman. His intelligence and resources make him a formidable foe for both heroes.
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.
A possible plot could be that they discover the pregnancy during a battle. Maybe some sort of alien energy affects them both, and they soon realize they're going to have a baby. Then they have to hide it from their enemies who might see it as a weakness. They'd also need to figure out how to combine their different powers and heritages to ensure a healthy pregnancy and birth.