One idea could be a crossover where Goku meets Superman. They could have a friendly sparring match to test each other's strength. Maybe they start off misunderstanding each other's motives but then realize they are both protectors of their respective universes.
A cool plot might involve a rift in space - time that pulls the Dragon Ball Z world and the DC Universe together. Vegeta could be at odds with Wonder Woman at first, seeing her as a rival in terms of strength and combat skills. The Justice League and the Z Fighters then discover that an ancient evil force from both of their universes' pasts has been awakened. They must learn to work together, with Gohan and Robin sharing their intelligence to figure out a plan. The Saiyans' transformation abilities and the Justice League's various powers like the Flash's speed would be crucial in the final battle against this evil.
I think Gohan and Martian Manhunter would make for an interesting duo. Gohan is a brilliant and powerful character who has a lot of potential. Martian Manhunter, with his telepathic abilities and shape - shifting, could teach Gohan new ways to use his powers. And Gohan could show Martian Manhunter the value of pure physical strength. Also, Trunks and Flash would be a cool pair. Trunks' time - traveling and sword - fighting skills combined with Flash's super - speed would create some really exciting action scenes. They could race each other or team up to outrun a powerful enemy.
Maybe there's a rift in the multiverse that merges parts of the Dragon Ball Z world and the DC Universe. The Z Fighters and the Justice League initially think they are enemies due to misunderstandings. For instance, when Goku first meets Batman, Batman might mistake Goku's carefree attitude for recklessness. But as they gradually figure out the situation, they team up to close the rift and fight off threats that are emerging from the merged worlds.
I really like 'The Fusion of Two Worlds'. In this fanfiction, the technology in Young Justice's world and the ki powers from Dragon Ball Z are combined in a unique way. It starts with a strange portal opening up and the characters slowly getting to know each other's abilities. There are some great character interactions, like when Robin and Gohan start comparing their detective and martial arts skills.
Well, in such a fanfiction, the story might start with a strange energy signal that the Justice League detects. It turns out to be from a Dragon Ball. As they investigate, they meet Bulma. She explains to them about the Dragon Balls and their power. Then they team up to search for the remaining balls. Along the way, they face challenges not only from the Dragon Ball villains but also from some of the Justice League's enemies who see this new alliance as a threat to their plans. The two groups have to learn to work together, with their different cultures and power sets, to achieve their common goal of collecting all the Dragon Balls and making a wish that will save both universes.
Well, it could be really epic. Imagine Goku teaming up with Superman. They both have super strength and a strong sense of justice. Goku's martial arts skills combined with Superman's various powers like heat vision could make for some amazing fight scenes against powerful villains.
Well, in Dragon Ball Z, power levels are measured in a more straightforward numerical way. Goku at his Super Saiyan levels has an extremely high power level. In the Justice League, Superman is one of the most powerful with his super strength, heat vision etc. In a fanfiction, you could say that Goku's Super Saiyan Blue form might be on par with Superman in terms of raw power, but Superman has other abilities like flight and x - ray vision that Goku doesn't. So it's a complex comparison.
One idea could be a crossover where Goku is accidentally transported to the Justice League's universe. He might initially be seen as a threat due to his power but then they realize he's a good - hearted fighter. They could team up to fight a common enemy like Darkseid who has somehow acquired the Dragon Balls and is using them for his evil plans.
The power - up moments. For example, when a Young Justice character witnesses a Saiyan going Super Saiyan for the first time. It's a moment of pure awe and it adds a new level of excitement to the story.