One idea could be exploring an alternate universe where Ben gets the Omnitrix at a much younger age and has to learn to control it while dealing with school bullies who are after his power. Another could be a story where the Omnitrix malfunctions and starts giving Ben alien forms that are hybrids of different aliens he already has access to.
Gwen is an obvious choice. She can bring her magic skills and her relationship with Ben to the story. Also, Grandpa Max, who has a lot of knowledge and experience that can be useful in the fanfic. Another good character could be Kevin, with his ability to absorb materials and his complex relationship with Ben.
I don't think 'Bad Ben' is a real story. Usually, such works are crafted by the writer's imagination to offer a unique and thrilling experience to viewers rather than being rooted in real-life events.
The 'bad ben real story' might be a very personal account of someone named Bad Ben. It could involve his journey through life, his dreams, and how he overcame obstacles. Maybe it's about his growth as a person, his family, or his career. But again, without further details, this is just speculation.
I'm not sure specifically what the 'bad ben true story' is about as there could be many different stories with that name. It might be about a person named Ben who has done some bad things, but without more context it's hard to say.