The Puppeteer could also be paired with Chloe. Chloe has her own issues and insecurities, and the Puppeteer could use that to her advantage. They could form an unlikely alliance where Chloe believes she's getting something out of it, like more popularity or power, while the Puppeteer is using her as a pawn in her larger scheme against the heroes.
Another good pairing could be with Lila. Lila is a master manipulator herself, and when paired with the Puppeteer, they could create all sorts of trouble for Ladybug and Chat Noir. They could play off each other's devious natures and come up with some really elaborate plans to deceive the heroes.
I think Ladybug would be an interesting character to pair with Robustus. Their opposing natures could lead to some great conflict and character development. Another good option could be Cat Noir. His carefree attitude could contrast well with Robustus's more serious nature. And then there's Alya. As a journalist, she could be curious about Robustus and try to understand him, which could create an interesting dynamic.
Ladybug and Chat Noir are obvious choices. Their dynamic is always interesting to explore further. You can show how they grow and develop as heroes. Also, the Puppeteer herself is a great character to focus on. Her motives and powers make her a complex character that can be delved into deeper in fanfiction.
Most likely, we'll see the Puppeteer as a central figure. Alongside her, Ladybug and Chat Noir are bound to be there as they always are to save Paris. Also, Alya might be involved as she often helps Ladybug. Since the Puppeteer has a history of using dolls, perhaps there could be a new character who is an expert in doll - making or some sort of antique doll collector who has some connection to the Puppeteer's powers or origin.
I think Sabrina could be paired well with Chloe in a fanfic. Sabrina is Chloe's sidekick in the show, but in a fanfic, their relationship could evolve. For example, Sabrina could start to stand up to Chloe and this could lead to a whole new dynamic between them. Also, Luka could be paired with Chloe. Luka's calm nature could contrast with Chloe's brashness and it could make for an interesting story of how they influence each other.
In Miraculous Ladybug Princess Fanfiction, Marinette is a central and amazing character. She combines her Ladybug powers with her princess status in creative ways. Tikki also plays an important role. As Marinette's Kwami, she gives advice not only about being Ladybug but also about handling the responsibilities of a princess. Another character could be Chloe. In some fanfictions, she might be a rival princess or a character who has to learn to accept Marinette's new status, which creates interesting storylines.
A really cool plot could involve the Puppeteer teaming up with other villains in the Miraculous Ladybug universe. They could form a sort of 'villain alliance' and plan a major attack on Paris. The heroes would then have to figure out how to break their alliance and defeat them. Also, perhaps the Puppeteer discovers a way to use the Miraculous powers for herself without having a Miraculous, which would be a huge threat to Ladybug and Chat Noir.
One idea could be exploring the emotional aftermath for the characters after the events of Puppeteer 2. For example, how Ladybug and Chat Noir's relationship might have changed. Another could be introducing a new villain who takes advantage of the chaos left behind. Maybe a new Miraculous holder could also be introduced in the fanfiction, adding a new dynamic to the story.
The kwamis would be really interesting characters to include. Plagg and Tikki could offer their unique insights and humor. Trixx could also be there to play some pranks or help Alix with her Miraculous - related problems. Their presence would add a touch of magic and fun to the fanfiction.
Obviously, Marinette and Adrien would be key characters. Marinette could be the host of the sleepover, and Adrien might show up unexpectedly, either as himself or as Chat Noir. Their interactions would be the focus, whether it's some cute and awkward moments between them.
Marinette is often really well - written in these fanfics. Since she has such a complex personality as both a clumsy girl and a powerful superhero, fanfic authors can explore different aspects of her character. Chat Noir / Adrien is also great. His charm and his insecurities can be delved into deeper after the reveal. And sometimes Alya, as Marinette's best friend, is written very well. She can be the one who helps Marinette deal with the new situation after the reveal.