Another plot could involve Xeno Goku getting stranded in a different anime world during the crossover. He has to adapt to the new rules and powers there while also trying to find a way back home. He could make new friends and enemies in this strange world.
Trunks is another good option. His time - traveling experience and sword - fighting skills could add a new dimension to the crossover. He and Xeno Goku could work together to prevent disasters in different timelines.
One idea could be Goku ending up in the DC universe and having a friendly spar with Superman. Their different power sources and fighting styles would make for an exciting encounter. Maybe Goku learns about Kryptonite and how it affects Superman, which gives him a new perspective on weaknesses.
One idea could be Goku Black crossing over into a modern-day Earth where he has to deal with advanced technology that he doesn't understand at first. Another could be a crossover with a different anime universe, like Naruto, where Goku Black's power clashes with the ninja abilities. Maybe he teams up with Naruto against a common enemy.
One idea could be Goku from Dragon Ball crossing over into a world like Fairy Tail and having a harem of the female mages there. Maybe he helps them in battles and gradually forms relationships with them.
One idea could be that Goku and Vegeta are transported to an alternate universe where they have to team up with their alternate selves to defeat a powerful new enemy that is a combination of all the foes they've ever faced. This would force them to not only work together but also understand different versions of themselves.
One idea could be Goku crossing over into a different anime universe, like the Naruto world. He could end up in a fight tournament there and show off his Super Saiyan Blue form. His ki attacks would be a new and strange concept to the Naruto characters.
One idea could be that Goku is transported to a different universe where he meets various female characters from different anime. They are all intrigued by his power and his pure-hearted nature, and a harem dynamic starts to form as they all want to be around him and train with him.
One idea could be a tournament where Goku and Naruto are both invited. They start off as rivals but then realize they have more in common as they face powerful opponents together. Another could be a situation where an enemy from Goku's universe somehow ends up in Naruto's world and they have to team up to defeat it. A third idea is that a magic spell or some kind of power - related accident causes their powers to be swapped, leading to comical and also challenging situations as they try to adapt to each other's abilities.
A Goku crossover with the Pokémon world could be really fun. Goku could try to catch Pokémon using his speed and strength. He might also team up with Ash to battle powerful Pokémon trainers. Or how about a crossover with the Digimon world? Goku could enter the Digital World and help the Digimon in their battles against evil Digimon using his energy attacks.
One idea could be a crossover with Harry Potter. Kid Goku could end up at Hogwarts and his martial arts skills would be a unique addition to the magical world. He might use his Ki blasts instead of magic spells in some situations.