Another possibility could be Chara. In undertale, Chara has a complex and somewhat malevolent nature. If they were in a pokemon crossover, they might find a way to manipulate pokemon or use their determination - related powers in a way that makes them extremely powerful. They could potentially form alliances with dark - type pokemon or use their knowledge of the undertale world to outwit opponents in the pokemon world.
Character interactions are also great. Imagine Frisk from undertale meeting Pikachu. Their personalities are so different. Frisk is this kind and empathetic character, while Pikachu is energetic and curious. Their meeting could lead to all sorts of comical or heart - warming situations. Maybe Frisk tries to communicate with Pikachu in the undertale way, and Pikachu responds in its own pokemon - like way.
Arceus from Pokemon and Omnimon from Digimon are both extremely powerful. Arceus is like a god in the Pokemon world, creating everything. Omnimon is a powerful Digimon formed by the fusion of WarGreymon and MetalGarurumon. If they were in a crossover, it's really hard to say who would be more powerful. It might depend on the situation and how their powers interact.
Another candidate could be Dialga from Pokemon. Dialga has the power to control time. In a crossover, if it could use its time - control abilities effectively against the Dragonball Z characters, it could be very powerful. For example, it could freeze time and then attack its opponents without them being able to react. But again, Goku has shown the ability to break through all kinds of limitations, so he might still find a way to defeat Dialga in the end.
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.
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.
One idea could be that the Pokemon are in the Underground world of Undertale. Maybe Pikachu could befriend Frisk and help them on their journey. The Pokemon could have unique interactions with the monsters there, like using their moves in battles against the monsters in a different way than in the Pokemon world.
Some of the Pokemon could take on the forms of Undertale characters or vice versa. For instance, a Gardevoir could take on the appearance of Toriel to help comfort the other characters. This would not only be a cool visual but also a way to blend the two universes on a deeper level. The personalities of the characters could also influence the behavior of the Pokemon or the transformed characters. There could be a lot of emotional moments and comical situations as a result of these integrations.
Ruby and Frisk would be a really interesting pairing. Ruby is full of energy and determination, and Frisk has that unwavering kindness. They could learn a lot from each other, especially in terms of how they approach difficult situations and make decisions.
Frisk could be a very interesting character to focus on. Frisk has the power of determination, which could be used in unique ways in the FNAF setting. They could befriend some of the animatronics, using their kindness and determination. Also, since Frisk is the player - controlled character in Undertale, it would be interesting to see how they adapt to the more dangerous and unpredictable world of FNAF.
I think Leonardo and Papyrus would make an interesting pairing. Leonardo's leadership and discipline could contrast with Papyrus' more naive and enthusiastic nature. They could learn from each other, like Leonardo teaching Papyrus some ninja moves, and Papyrus showing Leonardo how to have more fun. Another great pairing could be Donatello and Alphys. They are both the 'tech - smart' characters in their respective universes. They could collaborate on some crazy inventions that combine Undertale technology and Turtle - made gadgets.