The story could start with a strange energy signal that both Ben and the Young Justice team detect. They initially suspect each other but then realize they need to work together. Ben might transform into Four Arms to take on stronger foes in hand - to - hand combat, while Robin from Young Justice uses his detective skills to figure out the origin of the signal. As they progress, they discover that an ancient alien race is behind it all, and they have to combine their powers and wits to stop this race from taking over the world.
Well, the plot could involve Ben Tennyson and the Young Justice team teaming up to fight a common enemy like Darkseid. Ben could use his various alien forms to complement the powers of the Young Justice members. For example, Heatblast could help Superboy when dealing with cold - based threats.
A cool plot could be that a dimensional rift opens up and pulls some of the Young Justice characters into the Ben 10 universe. They then have to find a way to get back home. Along the way, they meet Ben and join forces with him. Ben shows them around his world, and they help him deal with some local threats. For instance, Aqualad could use his water - based powers in conjunction with Ben's Four Arms in a fight against a group of robotic enemies that are causing chaos in a city near Bellwood.
One possible plot could be that the Omnitrix malfunctions and sends Ben 10 to the Justice League's universe. The Justice League initially views Ben as a threat due to his alien forms. But as they learn more about him and the threat of an inter - dimensional villain, they team up. Ben's different alien forms offer unique skills that complement the League's powers, and together they fight the villain to save both universes.
The plot could involve Ben using his alien forms to help the Young Justice team in their missions. For example, he could transform into Heatblast to deal with a fire - based villain that the team is struggling with. His alien powers would add a new dimension to the team's capabilities.
One possible plot could be that a common enemy, like a powerful interdimensional villain, forces the Young Justice team and the Avengers to team up. They start off distrustful of each other, with the Avengers seeing the Young Justice members as inexperienced kids and the Young Justice team thinking the Avengers are too rigid. But as they face the villain's various attacks, they gradually learn to work together. For example, Superboy could team up with the Hulk in brute - force battles, while Robin and Iron Man use their intelligence to figure out the villain's weaknesses.
Well, one possible plot could be that Supergirl is somehow transported to the Young Justice universe. Maybe there's a dimensional rift caused by some villain's experiment. She then teams up with the Young Justice team to stop this villain from causing more chaos across different dimensions. They could learn from each other's skills and powers along the way.
One idea could be to have Ben Tennyson end up in the Young Justice universe by accident. Maybe his Omnitrix malfunctions during a fight and transports him there. He could then team up with the Young Justice heroes to fight a common enemy like the Light or some new villain that's a threat to both universes.
One possible plot could be that Naruto is somehow transported to the Young Justice universe. He teams up with the Young Justice team. Naruto's unique jutsu skills like the Rasengan could be used to fight the villains in the Young Justice world. Maybe they face a common enemy that requires both Naruto's ninja abilities and the superpowers of the Young Justice members to defeat.
One idea could be that Spiderman gets transported to the Young Justice universe. He teams up with the team to stop a common enemy like Vandal Savage, who has some new high - tech weaponry. Spiderman's unique abilities like web - slinging and his spider - sense would add a new dynamic to the team's combat strategies.
One possible plot could be that Subaru from 'Re:Zero' somehow gets transported to the world of 'Young Justice'. He might initially be confused but then use his 'Return by Death' ability to his advantage. For example, he could help the Young Justice team in battles by being able to predict enemy moves after dying a few times. His unique perspective on life and death could also influence the team's moral decisions.
In a Ben 10 and Justice League crossover fanfiction, there could be epic battles. Ben could use his alien forms to team up with Superman and take on powerful villains. For example, Ben as Four Arms could help Superman in a physical fight against a huge and strong enemy.