One great 'Naruto Crossover Overlord' fanfic is 'Naruto in the World of Overlord'. It has an interesting plot where Naruto is transported to the Overlord universe and has to adapt to its rules and power systems. His ninja skills create a unique dynamic in the new world.
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.
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.
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'.
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.
Character interactions are also unique. For example, Naruto's positive and determined personality clashes and then meshes with the often more complex and morally grey characters in the Overlord world. This can lead to some really interesting character development arcs, like a cynical Overlord character starting to believe in Naruto's ideals of friendship and hard work.
Ainz Ooal Gown is likely one of the most popular. His powerful and mysterious nature makes him a great character to crossover. He can bring his vast knowledge of magic and leadership from Overlord into the RWBY universe. Another popular one might be Albedo. Her loyalty and combat abilities can create interesting dynamics when interacting with RWBY characters. For example, she could form an alliance with a team in RWBY and use her skills to help them in battles.
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.
Ruby Rose is often a popular crossover character. Her positive attitude and powerful scythe - wielding skills can bring a unique dynamic to the Overlord universe. She might befriend some of the more benevolent characters in Overlord or cause chaos with her energetic nature.
One interesting concept could be the combination of different game worlds with the Overlord universe. For example, mashing up Overlord with a fantasy RPG world like Skyrim. Characters from Overlord might interact with the unique races and magic systems in Skyrim, creating new and exciting storylines.