Well, in these fanfics, Bulma might be an important character. She could use her intelligence to create some sort of device or plan to stop Evil Goku. Also, Piccolo would be there. His strategic mind and powerful attacks would be crucial in the fight. And of course, there might be new characters created specifically for the fanfic, like a mysterious sage who knows the secrets to defeating Evil Goku.
One interesting plot could be Evil Goku's origin. Maybe he's a result of some dark magic or an alternate dimension's influence. Another plot might involve his battles against the regular Z - fighters. He could have new and more devious fighting techniques.
Another way is that Goku could use the Spirit Bomb. He could gather energy from all living things on Earth and nearby planets. Android 21, being an artificial being, might not be able to withstand the pure energy of the Spirit Bomb. However, she could try to absorb the energy, but if Goku can overload her absorption capabilities, it would be his victory.
In a fanfiction scenario, Goku and Android 21's fight could attract the attention of other Z - fighters. Vegeta, for example, might be reluctant to help Goku at first but then realizes the danger Android 21 poses to the entire planet. Goku could also try to reach out to Android 21's good side, as he has a history of trying to redeem his enemies. This could add an interesting moral dilemma to the story, whether to fight or try to save her.
Claudia is not a character from the original Dragon Ball series. Goku is the main protagonist of Dragon Ball. He is a Saiyan sent to Earth as a baby. He is known for his powerful fighting abilities, his love for martial arts, and his kind heart. He has saved the Earth multiple times from various threats.
There's a fanfic called 'Goku's Hidden Power'. In this story, Goku discovers a new level of power within himself that even the Kais didn't know about. It delves deep into Goku's character, exploring how he copes with this newfound strength and the responsibility that comes with it. The action scenes are also very well - written.
In a fanfiction, Goku might be weakened due to a curse. He loses his Super Saiyan powers and has to start from scratch. This could lead to a great character - development arc. He might discover new ways to fight without relying on brute strength, like using his wits and strategic thinking more, and also learning new martial arts techniques from his human friends.
Perhaps a fanfiction where Vados senses a new threat approaching the universe. She enlists Goku to help her find a way to stop it. Along the way, they encounter strange new races and powers. Goku's simple but powerful approach to fighting combined with Vados' wisdom would make for an interesting dynamic as they search for a solution to this impending doom.
Goku's understanding of different universes and races could be deepened in fanfiction. Since Dragon Ball Super introduced the multiverse concept, fanfiction could explore how Goku interacts with and learns from beings from other universes, making him more worldly and less naive in some ways.
One of the interesting power - ups could be his Ultra Instinct form. In fanfiction, it might be further enhanced, like having different levels that are not shown in the original. For example, he could have an Ultra Instinct - Kaioken combination which would be extremely powerful.