To write a good Ben 10 and OC fanfiction, start with a solid idea. It could be something as simple as your OC getting caught up in one of Ben's adventures. Research is key. Look into the existing Ben 10 storylines, the relationships between characters, and the overall tone of the series. When creating your OC, think about how they will fit into this world. Are they a hero, a villain, or something in between? As for the writing itself, use vivid descriptions to bring the action and characters to life. For example, when describing an alien transformation, make it exciting and detailed.
Writing a great Ben 10 and OC fanfiction requires several steps. Firstly, immerse yourself in the Ben 10 world. Watch the shows, read the comics if possible. This will give you a feel for the style and the kind of stories that work. For your OC, consider their motivation. Why are they in the Ben 10 universe? What do they hope to achieve? Once you have a clear idea of your OC, start building the story around them. Incorporate elements from the Ben 10 series like the Plumbers or the various villains. Also, don't be afraid to add your own twists and turns to the story. This will make your fanfiction stand out from others. For example, you could introduce a new type of technology or a hidden power within the Omnitrix that your OC discovers.