Marinette, as Ladybug, could use her wits and courage. She could outsmart Lila in a public situation. Let's say Lila tries to embarrass Marinette at a big event, but Marinette, using her Ladybug - like charm and intelligence, turns the tables and reveals Lila's true nature to everyone.
In Marinette x Lila fanfics, a frequent theme is the exploration of their complex relationship. Since they are often at odds in the original show, fanfics might focus on how they overcome their differences. There's also the theme of hidden feelings. Maybe Marinette has some unacknowledged feelings for Lila beneath her initial dislike, or vice versa. And sometimes, there's the theme of a shared adventure that brings them closer together, like facing a common enemy in the Miraculous Ladybug universe.
One common way for Marinette to get revenge in fanfiction could be through her fashion skills. She could design something that makes Lila look foolish. Like creating a dress for an event that has a hidden message or design that mocks Lila's lies when she wears it. It's a more creative and less confrontational way of getting revenge, but still very effective in showing Lila that Marinette is not one to be trifled with.
One possible scenario in a fanfiction could be that Lila finally realizes the error of her ways and decides to make amends with Marinette. She might see how Marinette's kindness has always been genuine despite her lies, and they could gradually become friends. This would be a big character development for Lila.
A really interesting fanfiction idea could be that Lila and Marinette switch personalities for a day. This would be a comical yet thought - provoking situation. Lila would have to deal with Marinette's responsibilities and kindness, while Marinette might struggle with Lila's devious ways. It could lead to both of them having a new perspective on each other.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3) or FanFiction.net. There are often tags and search filters that can help you narrow down to Marinette x Lila fanfics. Some authors might also post their works on Tumblr or Wattpad, so it's worth checking those places as well.
One possible plotline could be that Lila spreads false rumors about Marinette at school, causing Marinette's friends to doubt her at first. For example, Lila might say Marinette stole something from her, which makes everyone look at Marinette suspiciously.
A popular revenge plot is Marinette using her Ladybug powers in a discreet way. Since she has the power of creation, she could create small 'accidents' that expose Lila's lies. For example, if Lila lies about being an expert in a certain field, Marinette could use her power to make things appear that prove Lila wrong. It's a unique take as it combines her superhero identity with her personal vendetta against Lila.
Lila lies a lot in fanfiction. These lies could directly target Marinette and make her life at school miserable. So, Marinette may move to get away from all that drama.
Well, it could be that Lila has managed to turn the teachers against Marinette too. In fanfiction, she might be so good at manipulating that she convinces the school staff that Marinette is a troublemaker. This, combined with the students' negative attitude towards Marinette due to Lila's lies, could lead Marinette to decide that moving schools is the best option.