Well, if we consider all the characters from both universes combined, it's hard to say for sure. Goku is obviously a top contender with his godly forms and limitless power potential. But then there's also characters like Whitebeard from One Piece. He had the power to cause massive earthquakes and was feared across the Grand Line. If he were to somehow gain access to Ki or some form of Dragon Ball Z - like power - up, he could be just as strong as Goku. And let's not forget about Vegito, who is a fusion of Goku and Vegeta. His combined power is off the charts, and in a combined universe, he would be a force to be reckoned with as well.
It's really hard to say. Goku in his Super Saiyan Blue form has incredible power and can destroy planets. But Naruto in his Six Paths Sage Mode also has amazing abilities. However, if we consider raw power, Goku might be more powerful as he can reach levels of power that can destroy entire solar systems. But Naruto's intelligence and his ability to strategize could give him an edge in a fight.
It's likely Goku. His Super Saiyan forms give him incredible power levels that far exceed most of the characters in One Piece. He can move at incredible speeds, has amazing strength, and can fire powerful energy blasts. Even Luffy in his Gear Fifth form would probably have a hard time against Goku at his full power.
It's hard to say, but Goku would be a top contender. His ability to constantly power up and reach new levels of strength like Super Saiyan God and Ultra Instinct is insane. But Ben in his Alien X form from the Omnitrix also has near - omnipotent powers. So it could really go either way depending on how the fanfiction writer sets up the battle conditions.
In a combined fanfiction universe, it could be Whis from Dragon Ball Super. He is an angel who is extremely powerful and has knowledge far beyond most characters. He could potentially use his knowledge of the multiverse and his own powers to outwit and overpower anyone. Although Sailor Moon has the power of the Silver Crystal and Goku has his Saiyan strength, Whis' ability to manipulate time and space, as well as his overall power level, might make him the most powerful character. However, it also depends on how the author of the fanfiction wants to balance the powers of the two universes.
It's likely Goku. His Super Saiyan forms give him incredible power, and his ability to constantly train and get stronger is unrivaled. He could easily defeat most of the Kung Fu Panda characters in a one - on - one fight.
Gohan in his Ultimate form could also be a very powerful character in this combined fanfiction universe. He has incredible strength and intelligence in combat. But on the RWBY side, Ozpin has a lot of hidden power and knowledge. Still, when comparing their power levels, Gohan's physical strength and energy projection abilities are on a different scale. He could potentially take on even the toughest Grimm with ease. So, overall, Gohan might be among the most powerful in this crossover scenario.
However, All For One could also be a very strong contender. His quirk allows him to steal and use other people's quirks. In a combined universe, he could potentially steal powers from Dragon Ball characters as well. Imagine him with the power of a Saiyan or some of the Dragon Ball energy - based attacks. It would make him an incredibly formidable foe.
Goku and Luffy would be really interesting. Goku is all about pure strength and the pursuit of becoming stronger through training, while Luffy is more about the adventure and his dreams. Their different outlooks could lead to some great conversations and also some funny moments, like when Luffy tries to eat Goku's senzu beans thinking they are some kind of food from his world. Another interesting interaction could be between Vegeta and Zoro. Vegeta is very proud and serious, and Zoro is a swordsman with his own code of honor. They could have some intense sparring sessions and also respect each other's strength.
Zoro and Vegeta would also be a cool pairing. Zoro is all about becoming the greatest swordsman and has a strong sense of pride. Vegeta is a proud Saiyan prince. They could start off as rivals, constantly trying to outdo each other in combat. But as they face tougher enemies together, they would start to respect each other's skills. Vegeta could teach Zoro some energy - based attacks to add to his swordsmanship, and Zoro could show Vegeta the value of discipline in a different way.
Well, if we consider that in the Sonic universe, there are characters like Shadow who has his own unique abilities and is very powerful. In a crossover, if he were to gain some of the Saiyan abilities like ki control, he could be a formidable force. But then again, Vegeta with his pride and combat experience wouldn't be one to back down. He might be able to figure out Sonic's speed patterns and counter them. So it's not easy to determine who would be the most powerful. It could also be a new character that emerges from the combination of the two universes' power sources.