I think it really depends on the context of the fanfiction. If it's set in the world of Overlord, Ainz might have an advantage because he knows the terrain and has his support system there. But if it's in Ben's world, Ben would be more familiar with the surroundings. Also, some of Ben's alien forms like Clockwork could manipulate time, which could be a huge advantage against Ainz. However, Ainz has his own time - related magic in some ways. So it's a very complex question with no easy answer.
It's hard to say. Ainz Ooal Gown has a vast array of powerful magic spells at his disposal. However, Ben when he transforms into Alien X could be extremely powerful as well. Alien X has reality - warping abilities. But Ainz has his intelligence and strategic thinking. So it could really go either way depending on the situation.
It could be really cool. Picture the powerful beings from Overlord in the world of Ben 10. Maybe Ainz Ooal Gown could use his magic against some of Ben's alien forms. The different power systems would create some interesting battles and interactions. For example, how would Ainz deal with an opponent like Four Arms? And how would Ben react to the undead hordes that Ainz commands? There are so many possibilities for epic crossovers in this fanfiction concept.
Ainz Ooal Gown would be a very interesting character to focus on. He has a complex personality and his vast power makes him stand out. In a crossover, seeing how he adapts to a different anime world's rules and cultures would be fascinating. He could be the catalyst for many interesting plot developments.
One idea could be to have the characters from 'Overlord' end up in a different anime world like 'Sword Art Online'. They could interact with the SAO characters, with Ainz Ooal Gown perhaps trying to establish his own guild in the SAO world. Another idea is to cross 'Overlord' with 'Naruto'. Picture the undead minions of Ainz in the Hidden Leaf Village, causing chaos and confusion among the ninja.
It's likely that Ben with the Omnitrix would be one of the most powerful. He has access to a wide variety of alien forms, each with their own unique abilities. For example, Heatblast could deal with cold - based threats in the Rosario Vampire world, and XLR8 could outrun any fast - moving vampires or enemies. However, some of the powerful vampires like Alucard in Rosario Vampire also have incredible strength, speed, and magical abilities. So it could be a close call between Ben in his most powerful alien forms and the top - tier vampires.
Well, it could be about a crossover in the Ben 10 universe that involves neglected or overlooked characters or storylines. Maybe it's a fan's attempt to give more spotlight to those parts that the official shows or comics didn't fully explore.
It could be Ben himself. Imagine him using his alien forms in the Naruto universe. His Heatblast form could be really useful against ice - based jutsu, and Four Arms could take on some of the physically strong ninja. He would bring a whole new element of power and chaos to the Naruto world, and his reactions to the different cultures and powers in Naruto's world would be interesting to explore.
The novelty. It combines two different fictional universes. For example, when Overlord crosses with another anime like Fairy Tail, you get to see magic from two very different perspectives interact.
One common theme is the exploration of Shalltear's power. Since she's a very powerful character in the Overlord universe, many fanfictions like to test her limits when she's in a crossover situation. Another theme is loyalty. Shalltear's loyalty to Ainz is a big part of her character, and in crossovers, this loyalty often gets challenged or reaffirmed in different ways. For example, in some crossovers, she has to choose between following Ainz's commands and doing what she believes is right in the new world she's in.
One idea could be an Overlord crossover with Sword Art Online. You could have the powerful beings from Overlord enter the virtual world of SAO and cause chaos among the players. They might see the game world as a new territory to conquer or just a place for some interesting 'experiments'.
Well, there's a 'Overlord Crossover Fanfiction' that combines it with 'Fullmetal Alchemist'. In this, the alchemic concepts of 'Fullmetal Alchemist' are pitted against the magic and power structures in Overlord. It's really cool to see how the characters from both worlds adapt to each other's rules. There's also a crossover with 'Attack on Titan' which brings in the element of the Titans into the world of Overlord, creating a lot of intense and unique battle situations.