A rogue scientist who has created a device that can nullify powers. He wants to use it on Ben, Gwen, and Kevin to prove his superiority. He's been experimenting on other aliens and humans, and his actions are starting to cause widespread panic. Ben, Gwen, and Kevin have to stop him before he can use his device on them and before he causes more harm to the galaxy.
An evil alien warlord from a far - off galaxy could be a great main villain. He could have an army of powerful alien creatures at his command. He might be after the Omnitrix, Gwen's magic book, and Kevin's Osmosian powers to become all - powerful. His forces could be causing chaos across the universe, and it's up to Ben, Gwen, and Kevin to stop him.
One possible plot could be that a new powerful alien threat emerges that neither Ben, Gwen nor Kevin can defeat alone. They have to combine their unique powers and skills. Ben could use his alien forms, Gwen her magic, and Kevin his Osmosian abilities. They start off not getting along well in the team - up, with some bickering about the best way to approach the enemy. But as the situation gets more dire, they learn to trust each other and work in harmony to defeat the foe.
The Highbreed could also serve as the main villain. They are a powerful and xenophobic race in the Ben 10 universe. In a crossover, they might view the Justice League's world as a place to expand their territory. They could use their advanced technology and large numbers to attack. Ben would have to convince the Justice League that the Highbreed are a serious threat and together they would need to find a way to stop the Highbreed's invasion, perhaps by using Ben's alien forms like Upgrade to hack into their technology and the Justice League's strategic planning.
Obviously, Ben could be the one to save Gwen. With his Omnitrix, he has all kinds of powers at his disposal to take on Kevin and rescue Gwen. He knows both of them well, so he would be highly motivated to stop Kevin and bring Gwen back safely.
Vilgax could be a great main villain. He has a long - standing rivalry with Ben and his presence would add a lot of tension. He could see Albedo as a useful tool or a threat depending on the situation. Another option could be an original villain created specifically for the crossover. Maybe a powerful alien entity that wants to use Albedo's knowledge and Ben's powers for its own evil purposes. A third choice could be Aggregor, who might be after some new power source that is related to both Albedo and Ben.
One common theme is friendship. Kevin and Gwen's friendship is often explored, showing how they support each other. Another theme is growth. Kevin's growth as a character, whether it's in terms of his powers or his personality, is frequently a part of these fanfics.
A really interesting fanfic is 'Beyond the Omnitrix: Gwen, Kevin and Ben'. This fanfic takes the story to a whole new level by exploring what lies beyond the use of the Omnitrix. It shows how Gwen's magic, Kevin's powers and Ben's alien forms can combine in unexpected ways. The character interactions are well - written, making it a must - read for fans of the trio.
It could be an evil scientist who has found a way to combine ghost and alien technology. He wants to use this to take over both the human world and the ghost zone.
Well, it's obvious that Ben and Gwen are the central characters. Ben is the one with the cool Omnitrix. He can turn into aliens like Heatblast or Four Arms. Gwen, his cousin, is no less important. Her magic powers range from creating force fields to shooting energy blasts. Together, they make a great team. Ben brings the alien - powered muscle, and Gwen brings the magic - infused intelligence. They face all kinds of challenges, whether it's an evil alien invasion or a mysterious magical anomaly, and they rely on each other to get through it all.
Well, a good fanfic in this regard needs to capture the essence of the characters. Gwen is smart and powerful with her magic, Kevin is the tough guy with his unique powers, and Ben has his Omnitrix. A fanfic that plays on their relationships, like their friendly rivalries or how they support each other, is great. And of course, an exciting adventure or mystery that they have to solve. It could be something related to an alien threat or a new magical mystery. For instance, if the fanfic has them exploring an ancient alien ruin where Gwen's magic is the key to unlocking the secrets, but they also need Kevin's strength and Ben's alien forms to overcome the traps, that would be really engaging.
Obviously, Dracula himself could be the main villain. He has all the classic powers like turning into a bat, super strength, and mind control. He could use these powers to try and take over the world or at least the area where Ben is currently located.