In some fanfictions, Snape has badass moments when he outsmarts Voldemort. For example, he manages to mislead Voldemort about the location of a crucial magical artifact. He uses his Occlumency skills to his advantage, hiding his true thoughts and intentions while presenting false information in a very clever way. This not only shows his intelligence but also his courage as he risks his life to deceive the Dark Lord.
Batman himself is obviously one of the most popular characters. He is the central figure and the source of the 'badass' factor in the fanfic. The Joker is also very popular as he provides a great contrast to Batman with his chaos and madness. Harley Quinn is often included as well, with her complex relationship with the Joker and her own brand of insanity. Another popular character is Robin, who represents the sidekick and the future of Batman's legacy.
Well, in 'batman badass fanfic', there might be the idea of Batman having some extraordinary combat skills. He could be shown using martial arts from all over the world in a more seamless and deadly way. Maybe he has a special move that he developed himself to take on multiple opponents at once. And then there could be a concept of a secret society within Gotham that Batman has to infiltrate. This society could have its own set of rules and power dynamics that Batman has to navigate through, adding an extra layer of mystery and danger to the story.
One interesting aspect could be the unique interpretations of Batman's character. Fanfics might explore a darker or more complex side of him that we don't always see in the official comics or movies. For example, they could show his internal struggles in more depth.
One of the best moments could be when Batman manages to outwit Harley in a battle of wits. He uses his knowledge of her psychology to predict her moves. For instance, if Harley tries to set a trap using her knowledge of Arkham's layout, Batman quickly figures it out and turns the tables on her.
I'm not sure of specific titles off - hand, but you can start by looking on fanfiction websites. Search for ones with high ratings and lots of reviews. Usually, those are the better ones.
There could be a moment where Percy stands up to an unjust authority figure in the fanfiction world. He defies them with such confidence and charisma that it makes him seem like a total badass. Or perhaps he dives into a dangerous, unknown realm to save someone, showing his fearless and selfless side which is very badass.
One possible badass moment could be when bella stands up to a powerful alpha wolf. She shows no fear and uses her sharp tongue to put the wolf in its place.
One badass moment could be when Ezra single - handedly takes on a group of stormtroopers in a narrow corridor. Using his lightsaber and the Force to deflect blaster bolts back at them, he cuts through their ranks like a hot knife through butter. Another might be when he uses his Force powers to manipulate a large ship's controls from a distance to prevent it from crashing into a rebel base.
One key moment is when Catwoman saves Batman's life. It shows that despite their differences, she cares for him. Another is when they share a tender moment on a rooftop, looking out over Gotham. It's a moment of connection between them.