One idea could be a crossover where the Miraculous heroes and Ben 10 team up to fight a common enemy. Maybe an alien villain that is immune to the powers of the Miraculous but Ben's alien forms can counter. Another could be a situation where Ladybug's Lucky Charm combines with one of Ben's alien gadgets to create a super - weapon. And a third could be a story where Ben gets akumatized and the Miraculous heroes have to figure out how to save him without using brute force as his alien forms are very powerful.
Well, a cool plot could be that the Miraculous kwamis are intrigued by the Omnitrix. They decide to study it and in the process, accidentally create a rift in space - time. This leads to the characters from both universes having to work together to close the rift. Or perhaps Hawk Moth somehow gets a hold of a piece of Omnitrix tech and tries to use it to enhance his akumas. The Ben 10 characters then have to help the Miraculous heroes stop Hawk Moth before he creates an unstoppable akuma. Also, a story where the characters swap powers could be interesting. Ben uses the Miraculous powers while the Miraculous heroes get to use the Omnitrix for a while.
One idea could be a story where the Peacock Miraculous has a unique malfunction that causes it to create unexpected akumas. For example, instead of creating the usual villains, it creates akumas that have the power to spread positive emotions but in a chaotic way that still disrupts Paris. Another idea is a fanfiction where the holder of the Peacock Miraculous has to team up with Ladybug and Chat Noir to fight against an ancient evil that is specifically drawn to the power of the Peacock. This could involve exploring the history of the Miraculous and its connection to this new threat.
One idea could be that during Halloween, the Miraculous holders have to deal with akumas that are inspired by classic horror movie monsters. For example, an akuma that turns into a vampire - like creature, making people fall under its spell and causing chaos in the city. Another plot could be a Halloween party where the villains try to steal the Miraculous in disguise, adding an element of mystery and danger.
One idea could be that the fox Miraculous has some unique powers that are not fully explored in the original. For example, it can create illusions not just of objects but also of emotions, which the fox - themed hero uses to calm down akumatized villains.
One idea could be Carapace getting a new power upgrade and having to learn to control it while facing a powerful new villain. Maybe he teams up with a new Miraculous holder.
A plot where there is an international Miraculous team-up. Heroes from different countries with their own Miraculous come together to face a global threat. They have different fighting styles and powers, and it's a challenge for them to work together against a common enemy in this showdown.
One idea could be Multimouse getting lost in an alternate dimension where the rules of the Miraculous are different. She has to figure out how to use her powers in new ways to get back home.
One idea could be that the Miraculous Phoenix has the power to heal not only physical wounds but also emotional traumas. The story could follow a character who is deeply scarred by past events and is chosen by the Phoenix Miraculous. As they learn to use its powers, they gradually heal themselves and those around them.
One idea could be that the characters from RWBY and Ben 10 universes team up to fight a common enemy that threatens both their worlds. For example, a powerful alien race in the Ben 10 world that has somehow found a way to access Remnant (the RWBY world) and is causing chaos.
Maybe in the fanfiction, Attea is in trouble on her home planet and Ben, being the hero he is, goes to help her. Along the way, they discover a long - lost secret about their two species that changes their relationship forever. This could involve some cool battles and new alien forms for Ben to use.
One idea could be that Ben uses his Omnitrix to transform into a Pokemon - like form. For example, he could turn into a fire - type alien that has the abilities of a Charizard. Another plot could involve Ben and Ash Ketchum teaming up to stop a powerful villain who is trying to capture all the Pokemon and use the Omnitrix for evil purposes. Maybe there's a device that can fuse Pokemon with Ben's aliens, creating super - powerful hybrids.