One idea could be that Ben has to adapt to the daily life of the alien he's stuck as. For example, if he's stuck as a Four Arms, he has to deal with constantly breaking things because of his size and strength. Another could be that he has to find a way to communicate with his friends and family in his alien form, which might be difficult if the alien has a different language or way of expressing itself.
In this 'Ben 10 Stuck as Alien Fanfic', a great plot could be that Ben is stuck as an underwater alien. He has to learn to survive in the ocean environment, which is completely new to him. He discovers new allies and enemies in the ocean. His friends on land are trying to find a way to help him, but they face many difficulties as they don't fully understand the underwater world. Ben also has to deal with the fact that his alien form has some instincts that he has to control, like the urge to hunt certain sea creatures.
One idea could be exploring Alien X's internal conflict between Bellicus and Serena in a new situation. For example, when faced with a moral dilemma on a planet where two species are at war and both have valid reasons for their actions. Another plot could be Alien X having to deal with a powerful new enemy that can somehow disrupt his omnipotent powers. Maybe this enemy has the ability to split Bellicus and Serena's consciousness further, causing chaos within Alien X.
It could be an alien bounty hunter. This bounty hunter has been hired to capture Ben in his stuck - as - alien form. The hunter might have some special gadgets or powers that make it difficult for Ben to escape. And he's not interested in Ben's well - being, just in getting the reward for bringing him in.
A really interesting plot could involve a time - traveling aspect. Ben and Julie accidentally travel back in time to when Ben first got the Omnitrix. They have to be careful not to disrupt the timeline while also trying to find a way back to their own time. Along the way, they could meet younger versions of characters they know and have some really fun and emotional interactions. This could also lead to Ben learning some important lessons about his powers from his past self.
Well, you could write about the origin stories of some of the aliens in more detail. Maybe there are secrets about how Four Arms became so strong that haven't been fully explored. Also, a fanfic could focus on the relationships between the aliens. For instance, do they have a hierarchy or a social structure among themselves? And then there's the idea of an alien form going rogue and Ben having to deal with it in a unique way, not just by using another alien form to fight it.
One idea could be that an alien vampire infiltrates Ben's team. It pretends to be a friendly alien at first but then starts to slowly drain the energy of the other aliens. Ben has to figure out a way to expose it without endangering his friends.
First, focus on the character development. Show how Ben changes mentally and emotionally while stuck in alien form. Second, create interesting conflicts. For example, he could have trouble interacting with his family or friends. Third, describe the alien form in detail. Let the readers really understand what it's like for Ben. For instance, how does it affect his senses? His movements?
Another plot could be that a new villain emerges who has the power to control both human and Myaxx technology. Ben and Myaxx must figure out a way to break this control and stop the villain from taking over the galaxy. They start by gathering intelligence on the villain's lair and formulating a plan that utilizes Ben's shape - shifting abilities and Myaxx's knowledge of her own technology.
One idea could be that as a girl, Ben has to face different social challenges while still using the Omnitrix to save the day. For example, some might underestimate her because of her gender, but she proves them wrong with her heroic deeds.
One idea could be that Ben, using his alien forms, has to battle Dracula's minions in a spooky castle. Maybe he teams up with some local vampires who oppose Dracula's tyrannical rule. Another could be that Dracula tries to turn Ben into a vampire to use his alien powers for his own evil deeds.
A plot could involve a group of young Highbreed who are curious about Earth and its cultures, and they secretly befriend Ben. This would lead to a series of adventures where they have to hide their friendship from the more traditional and hostile Highbreed. They could learn a lot from each other, and Ben could teach them about the value of diversity and cooperation.