It's a tough call. Goku has his Super Saiyan forms and incredible combat power. He can destroy planets with his energy blasts. But Yugi has the power of the Pharaoh and his Millennium Puzzle. If he can manage to outwit his opponents in a duel, he can banish them to the Shadow Realm. However, in a direct physical fight, Goku would likely be more powerful. But if the situation was about strategy and using unique powers in a non - combat way, Yugi could be very dangerous.
Well, in a Yu - Gi - Oh Dragon Ball Z crossover fanfiction, the most powerful character could be a combination of both universes. Imagine a character who has the ability to use ki like a Saiyan and also has the power to duel like a Yu - Gi - Oh master. But if we have to pick from the existing characters, Whis from Dragon Ball Z is extremely powerful. He can manipulate time and has incredible combat abilities. Against the Yu - Gi - Oh characters, he could probably use his time - stopping ability to prevent them from making any moves in a duel or a fight. However, Yami Yugi also has his own set of powerful abilities, like his mind - reading and his connection to the ancient Egyptian magic. So it really depends on how the crossover is set up and what kind of powers are allowed to be used.
I think it would be a toss - up between Seto Kaiba and Gohan. Seto Kaiba has his high - tech cards and his own determination to be the best. He could potentially create some really powerful combinations. Gohan, on the other hand, has his Saiyan powers and his intelligence. If he could combine his fighting skills with an understanding of the Yu - Gi - Oh cards, he could be extremely powerful. But ultimately, it depends on how the crossover is written and the rules that are set for the encounter.
Yami Yugi from Yu - Gi - Oh is also a strong contender. His Millennium Puzzle gives him access to powerful magic and ancient knowledge. In a crossover, he could use his skills to outwit Pokemon trainers. He might be able to predict their moves and use his cards in ways that would give him an advantage against the Pokemon. He could also form a bond with some of the more intelligent Pokemon and use their powers to enhance his dueling abilities.
It could be Naruto. His huge chakra reserves and his ability to access the power of the tailed beasts would give him an edge. He could potentially use his chakra to power up Yu - Gi - Oh cards in ways no one else could. Also, his ninja skills like speed and stealth could be used during duels in unexpected ways.
It's hard to say for sure, but Naruto could be really powerful. His ability to create an unlimited number of Shadow Clones could give him an edge in a Yu - Gi - Oh duel. He could use the clones to strategize and overwhelm his opponents. However, Yugi has the power of the Millennium Puzzle and his strong connection with the spirit world. So, it really depends on how the crossover is written and what rules are applied.
Then there's Albus Dumbledore. His vast knowledge of magic and his powerful spells, such as the ability to perform powerful defensive magic and his wisdom in handling magical artifacts, could make him a force to be reckoned with. In a crossover, he could potentially study the Millennium Items and find a way to use their power in harmony with his own magic, making him a very powerful character in the combined universe.
It could be Yami Yugi. He has the power of the Millennium Puzzle and is an extremely skilled duelist. In a crossover, his ability to strategize and his connection to the ancient Egyptian magic within the Yu - Gi - Oh world could give him an edge. He could potentially use his skills to outwit the dark wizards in the Harry Potter universe. His confidence and the power of his cards could make him a formidable force against even the likes of Voldemort.
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.
It's hard to say, but Goku would be a top contender. His ability to constantly increase his power level and learn new techniques would make him a force to be reckoned with, even in a world with Pokemon. He could potentially use his Ki to enhance the abilities of any Pokemon he teams up with.
If we consider the potential of power - up in a crossover, it might be a new form of Goku. Imagine if Goku were to combine the power of the Saiyan God form with some of Devilman's demon - like abilities. He could become an entirely new and extremely powerful entity. But then again, Devilman has the potential to merge with other powerful demons in his world. So, in a sense, it could be either Goku with his new form or a super - powered Devilman depending on how the fanfiction unfolds.
Aizen Sousuke is another character from Bleach who could be in the running. His intelligence and his hogyoku - enhanced powers made him a formidable foe. In a crossover with Dragon Ball Z, if he were to face someone like Frieza, he could use his illusions and mind - games to gain an advantage. Frieza is powerful but not as mentally cunning as Aizen. However, if Frieza were to transform into his final form quickly and catch Aizen off - guard, Frieza could potentially win. So again, it depends on how the fight unfolds and who can utilize their powers more effectively.