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.
In my opinion, it's highly unlikely. Goku has mastered multiple forms and techniques that give him a wide range of powers. Saitama's one-punch style might not be effective against Goku's diverse skills and battle experience.
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.
I don't think there's a clear winner. Both Manga Goku and Manga Saitama have unique and powerful abilities. It could come down to strategy, luck, or even the author's imagination!
Another theme could be the clash of different universes. Amazo is from the DC universe and Saitama is from One Punch Man. Fanfics might play around with how these two different universes' rules and powers interact when these two characters meet. Also, there could be themes related to respect and rivalry. Saitama is often very nonchalant about his power, while Amazo is a complex android with various abilities. How they view each other in the fanfic can create interesting storylines.
Saitama would win. He has shown incredible strength with just one punch. His power seems limitless, and in a fanfiction scenario, his simplicity and raw power would likely overpower Jiren's more complex abilities.
One possible plot twist could be that Jiren discovers a way to nullify Saitama's strength. Maybe he finds some sort of energy - draining technique that weakens Saitama over time. Another could be that Saitama holds back for some reason, like he wants to see the full extent of Jiren's power, and in doing so, he gets into a real struggle.
A 'bardock xeno fanfic' has the potential to be a great piece of fan - created content. Since Bardock is such an iconic character, fans might be eager to read about his exploits in a Xenoverse - inspired world. The fanfic could show Bardock's growth as a character, how he adapts to new situations and challenges. It might also play with the idea of different versions of Bardock co - existing or interacting. This could open up a whole new narrative for fans to enjoy, with the added allure of the Xenoverse elements.
In a Saitama vs OC fanfiction, a plot twist could be that the OC has the power to make Saitama lose his strength. However, the OC doesn't want to use this power because they admire Saitama and want to test their own strength against him fairly. Another interesting twist could be that the OC is a part of a bigger plan by some mysterious organization. They use the fight against Saitama as a distraction while they carry out their real objective elsewhere. And as the fight progresses, Saitama realizes this and has to decide whether to continue the fight or go after the real threat.