I think Zeno would be a really tough opponent. Zeno has the power to erase entire universes, and a Goku and Goku Black fusion, despite being extremely powerful, would have a hard time against such a being with god - like powers.
It's really hard to say. Goku has the power to destroy planets and reach incredible levels of strength with his Super Saiyan forms. However, Naruto has the power of the tailed beasts and his own sage mode which gives him a huge boost in power. And Sonic, while he may not have the raw power like the other two in terms of destruction, his speed is so great that he could potentially outmaneuver both of them. So it really depends on the situation and how the author writes it.
It's debatable. There are many strong fictional characters, and it depends on various factors like powers, abilities, and the context of their stories.
Goku's ultimate form in the manga is Ultra Instinct. This state grants him enhanced combat abilities and reflexes. It's a breakthrough that showcases his potential and is a key factor in his toughest battles.
It's really hard to say. Ben at his strongest has access to some incredibly powerful alien forms. But Goku at his strongest can literally destroy universes. However, if Ben could transform into an alien with reality - warping powers, he might have a chance. But Goku's speed and combat experience are also very high. So it could go either way depending on the situation.
In general, it's a bit of a toss-up. The strength of Manga Goku and Anime Goku can vary depending on the specific arcs and battles. Sometimes, it might seem like one is stronger in a particular situation, but that could change in another.
Well, Vegeta would be a likely character. He might be initially suspicious of the female Goku. Maybe he thinks she's a threat or just can't believe there's another Goku - like being. He could be there to add some comical moments as he tries to understand the situation.
Another possible main character could be the villain that forces the two Gokus to meet. This villain could be a new, super - powerful threat that the two Gokus need to deal with. Their meeting becomes a crucial part of the story to defeat this powerful foe.
One of the characters who could betray Goku is Piccolo. Although they've been allies for a long time, in fanfiction, things can change. Perhaps an ancient evil force takes control of Piccolo's mind and makes him turn on Goku. Or it could be Krillin. He might be influenced by an outside force that convinces him Goku is becoming too dangerous. Also, don't forget about the Kais. If there's some sort of power imbalance or a threat they perceive from Goku, they might betray him to maintain the order of the universe in the fanfiction.