Vandal Savage is also a possibility. He has a long - standing enmity with the heroes. Maybe he has a new plan that involves using the resurrected heroes for his own evil purposes, or he's trying to stop their resurrection because he fears they'll thwart his future plans.
A new villain could be introduced. Maybe a rogue scientist who has been experimenting with life and death and sees the resurrected heroes as perfect specimens for his unethical experiments. He could be creating an army of undead - like creatures and the Young Justice team has to stop him before he unleashes this new threat on the world.
Vandal Savage could be a great main villain. Since he has a long - standing history in the Young Justice universe, he could be using the chaos of Endgame to his advantage. He might be secretly manipulating events behind the scenes to further his own goals of world domination.
The Court of Owls would be a great main villain. They are a powerful and secretive organization in Gotham. Their connection to Gotham's history and their shadowy nature could pose a huge threat to both Young Justice and Batgirl. They might be after some meta - human power or trying to take over Gotham in a new way.
Lex Luthor could be a great villain. He's always interested in taking down the Justice League and its affiliates. He might see the clone as a way to disrupt the Young Justice team and gain an advantage over Wonder Woman.
It could be a future version of an existing villain who has somehow gained even more power. For example, a more advanced and menacing version of the Light. They might be the ones causing the future problems that Future Robin is trying to prevent, and their actions in the present are just the start of their grand plan.
Sportsmaster would be a great villain. He's a skilled fighter and strategist, and he could target the apprentice specifically to get to the Young Justice team. He could also be training his own apprentice to go up against the Young Justice apprentice, creating a rivalry between the two.
Darkseid as a vampire - like being. He could come to Earth and start turning people into his vampire minions. His already formidable powers combined with vampiric abilities would make him a terrifying foe for the Justice League.
Brainiac would be a great choice. He has advanced technology that could be a huge challenge for the OC gamer. The OC might have to use their gaming knowledge to outwit Brainiac's complex systems and plans. For instance, if Brainiac tries to assimilate the world's knowledge, the OC could use their strategic gaming skills to disrupt his data - collecting devices.
Darkseid would be a great main villain. He's already a powerful and well - known foe in the DC universe. He could be the one who starts collecting the Infinity Stones - like items to gain ultimate power and rule over all universes. His army could also be involved, making it a large - scale war for the Justice League.
It could be Eggman. He might team up with some of the Justice League's villains, like Lex Luthor. Eggman could bring his mechanical creations and knowledge of chaos emeralds, while Luthor provides his strategic mind and resources. Together, they could pose a huge threat to both Sonic and the Justice League.
The Highbreed could also serve as the main villain. They are a powerful and xenophobic race in the Ben 10 universe. In a crossover, they might view the Justice League's world as a place to expand their territory. They could use their advanced technology and large numbers to attack. Ben would have to convince the Justice League that the Highbreed are a serious threat and together they would need to find a way to stop the Highbreed's invasion, perhaps by using Ben's alien forms like Upgrade to hack into their technology and the Justice League's strategic planning.