Transformation is a big theme. Since he has the ability to change his appearance, fanfics often play with this aspect, showing different forms he can take and the consequences of those changes. Revenge is also sometimes a theme, as he has his own grudges in the original stories.
Some fanfics might put them in an alternate universe scenario. Maybe in a world where they are part of a superhero team together. Cassandra could be the stealth and combat expert while Basil could bring something unique to the table, like a knowledge of some arcane or forgotten arts. The fanfic could explore how they grow as characters within this new team dynamic.
There's also 'Basil Karlo: Redemption'. It focuses on the idea of Basil Karlo seeking redemption for his past actions. The character development in this fanfic is quite remarkable, and it gives a fresh perspective on the character.
Some specialized Batman or DC Comics fanfic communities or forums might also be a good source. Members often share their own fanfics or know of great ones that are not as well - known on the bigger platforms. You can interact with other fans there and ask for recommendations specific to Cassandra Cain and Basil Karlo.
One of the best Clayface stories is his origin story. It shows how he became the shape - shifting villain. His transformation from an actor into a clay - like being with the ability to mimic anyone is really fascinating.
You can try exploiting his weaknesses. Clayface often has issues with maintaining his form or being vulnerable to certain substances. Figuring out those weaknesses can give you an edge.
Writing or seeking adult fanfiction involves inappropriate and often unethical content. It is better to focus on family - friendly or general - audience Clayface fanfiction that can be found on many mainstream fanfiction platforms. These usually explore his character, powers, and his role in the Batman universe in a more positive and acceptable way.
Another possibility is that Clayface somehow gets transported to the Naruto universe. The shinobi in the Naruto world would be very confused by his abilities. Clayface could try to blend in by mimicking the appearance of different shinobi, but his lack of chakra would give him away. Naruto might see through his disguise easily due to his own perceptive skills.
The fact that he's a villain but also has a sort of tragic backstory is another aspect. Fanfic can play with this duality. For example, some might show him as a sympathetic character trying to redeem himself, or they can explore his descent into villainy further. In a lot of fanfic, we get to see his relationships with other characters like Batman or other Gotham villains in a new light, which is really cool.
A very notable Clayface story is when he was used as a pawn in a larger scheme by a more powerful villain. He was manipulated into attacking certain targets in Gotham. His internal struggle between his own desires and being controlled by others was well - explored in this story. His shape - shifting abilities were also used in very creative ways, like creating entire false landscapes to trap Batman and other heroes.