Goku would be really excited to meet all the different heroes in the DC universe. He'd probably want to spar with everyone right away. Flash would be intrigued by Goku's ability to move at high speeds using his Ki. They could have a friendly race or competition to see who's faster in different situations. At the same time, Piccolo could team up with Martian Manhunter. They both have the ability to sense things from a distance and could use their skills to detect threats to both universes.
Goku would probably be really excited to meet Luffy. He'd be curious about Luffy's rubber powers and would want to have a friendly sparring match right away. Luffy, on the other hand, would be in awe of Goku's strength and would see him as a great ally. He'd probably ask Goku to join his crew, but Goku would decline because he has his own friends and family in Dragon Ball world.
One idea could be a battle between Goku and Superman. They could start off as rivals, each thinking their own planet needs more protection. As they fight, they gradually realize they have more in common than they thought, like their strong sense of justice. Then they team up to face a common enemy, like Darkseid and Frieza working together.
Goku would probably be very excited to meet Naruto. He'd be interested in Naruto's unique abilities and might immediately challenge him to a friendly sparring match to test their powers. Naruto, on the other hand, would be in awe of Goku's Super Saiyan transformations and might try to learn from him. They would likely bond over their shared love for fighting strong opponents.
If characters from different universes in this fanfiction were to interact, it could be really chaotic. For example, a character from a more technologically advanced universe might be completely baffled by the ki - based powers in the Dragon Ball Z universe. They could try to analyze it with their technology, which might annoy the DBZ characters. On the other hand, a DBZ character like Goku might be intrigued by the different fighting styles and abilities of characters from other universes. He would probably want to spar with them right away to test his own strength. Vegeta, being the proud Saiyan he is, might initially be dismissive of characters from other universes but then see them as a challenge to overcome.
Batman would be really interesting. Korra, being used to a world with clear good and bad, could be intrigued by Batman's morally gray methods. Their interaction could involve Korra trying to understand why he doesn't use more lethal force against his enemies, and Batman being fascinated by her bending abilities and how she uses them for both combat and peaceful purposes.
Some characters might be inspired by the concepts. For instance, if a fanfiction has a really cool new power - up idea for Gohan, he might think about how he could develop in a similar way in his own world.
Vegeta would also be a major character in these interactions. Their Saiyan bond could lead to different scenarios. Maybe Vegeta would be initially angry that Nappa survived but then come around to the idea of having him as an ally again. It could also be a source of conflict as they might have different ideas on how to handle certain situations.
In a more extreme scenario, Deadpool could end up in Arkham Asylum and think it's a new kind of S.H.I.E.L.D. facility. He'd start interacting with the inmates there, and Batman would have to step in to deal with the chaos Deadpool is causing. Deadpool would see Batman as this dark and brooding figure and keep trying to get him to lighten up.
Vegeta can be a really interesting crossover character. His pride and his journey to become stronger can be paralleled with some of the characters in Naruto. When he meets Sasuke, for example, there can be a clash of their strong - willed personalities which makes for a great story.