An original villain created just for the fanfic could be a powerful cosmic entity. This entity could be jealous of Captain Marvel's power and the Avengers' unity. It might try to break them apart and take over the universe.
Thanos could still be a likely villain. Even if he was defeated in the official storyline, in a fanfic he could return more powerful or with a new plan. His obsession with the Infinity Stones makes him a great overarching threat.
Annihilus could be a likely villain. He is a powerful being from the Negative Zone. In the fanfiction, Annihilus could be drawn to Earth because of the energy signature created when the Avengers and Captain Marvel meet. He sees Earth as a prime target for conquest. His powerful cosmic control rod gives him an edge in battle. The Avengers and Captain Marvel have to quickly learn about his weaknesses and use their combined powers to stop him from destroying Earth and spreading his reign of terror across the universe.
In a 'Captain Marvel Meet the Avengers' fanfic, there could be an epic showdown against a powerful villain. Captain Marvel's immense power combined with the Avengers' diverse skills would make for an amazing battle. For example, she could team up with Thor to take on an enemy that has the ability to control electricity. Their combined strength of her photon blasts and his lightning strikes would be a sight to behold.
There could also be a story where Captain Marvel has to prove herself to the Avengers. She might be seen as an outsider initially. So she has to show her worth through her actions. She could single - handedly take on a group of powerful villains to gain the Avengers' respect, and then they all work together towards a common goal.
In this fanfic, the main antagonist could be a scientist who has been corrupted by his own experiments. He creates some sort of energy - based monsters that are immune to normal attacks. Captain Marvel and the Avengers have to figure out how to stop these creatures and the mad scientist behind them.
She could meet a very smart science teacher who is intrigued by her powers and wants to study them scientifically.
One possible plot could be that the Avengers are facing an extremely powerful new enemy that they can't seem to defeat. Captain Marvel arrives on Earth just in time. At first, there are some misunderstandings and clashes of egos among the Avengers and Captain Marvel. But as they start to work together, they realize each other's strengths. Captain Marvel's raw power combined with the Avengers' teamwork strategies slowly turn the tide of the battle. Eventually, they defeat the enemy and Captain Marvel decides to stay on Earth for a while to help the Avengers train for future threats.
Thanos could still be a great antagonist even in a fanfic. He could come back with a new plan to obtain the Infinity Stones again. His powerful and menacing presence would create a high - stakes situation for Captain Marvel and the Avengers to face.
Yes, Captain Marvel is part of the Avengers in the comics. She's a powerful hero who often teams up with them to save the world.
No, Captain Marvel isn't typically considered the leader of the Avengers in comics. The leadership role often changes among various characters depending on the storylines and events.
The Green Goblin could be a great main villain. He has a long - standing feud with Spiderman, and when the Avengers get involved, it could make the situation even more complex. His flying glider and pumpkin bombs would pose a serious threat to both Spiderman and the Avengers.