One common theme is power struggle. Since all three characters - Harry Potter, Severus Snape and Lord Voldemort - are associated with different levels of power in the original series. In fanfiction, this power struggle can be explored in new ways, like in a different magical setting or with altered character abilities.
The X-Men are part of the Marvel Comics lineup. They have their own unique place within the Marvel multiverse, with a dedicated fan base and a significant impact on the comic book world.
X-Men is not associated with DC Comics. It's a Marvel creation. DC and Marvel have their own unique superheroes and comic book worlds that are independent of each other.
Sure. 'The Prince's Shadow' is a great one. It delves deep into the complex relationships between Harry Potter (hp), Severus Snape (ss) and Lord Voldemort (lv). The story has some really interesting plot twists and the character development is well - done.