Perhaps in the 'avengers of hydra fanfiction', Hydra has developed a new super - weapon that can neutralize the Avengers' powers one by one. The story could follow the Avengers as they scramble to find a way to counter this weapon while also dealing with Hydra's attacks on various cities. Or, there could be a plot where a powerful Hydra agent uses magic to possess some of the Avengers and make them do Hydra's bidding, and the remaining Avengers have to find a way to break the spell.
Well, a possible plot could be that the Hydra experiment was actually a cover - up for a much larger and more sinister plan. The Avengers discover that the experiment was just the tip of the iceberg and they have to race against time to stop Hydra from unleashing something far worse. It could also be interesting if the experiment somehow gives an ordinary person the ability to see into the future, and that person becomes a key figure in the battle between the Avengers and Hydra.
One idea could be a character with the Hydra Bloodline having the ability to split into multiple versions of themselves during battles, like the Hydra in mythology. Each split could have a different combat skill, making it a very unique fighting style.
One plot idea could be that Captain Hydra, in a universe where he exists, tries to recruit Tony for his evil plans by appealing to Tony's scientific curiosity with some dark technology. Another could be a scenario where Tony, initially unaware of Captain Hydra's true nature, teams up with him for a project but slowly discovers the truth and has to fight against him. Or perhaps a story where they are both caught in an alternate dimension and must work together, reluctantly in Tony's case, to find a way back home while Captain Hydra keeps trying to undermine Tony's good intentions.
One idea could be a crossover where Hydra discovers the wizarding world in the Harry Potter universe and tries to use magic for their evil purposes. The Avengers somehow get wind of this and team up with Harry Potter and his friends to stop Hydra. Maybe they have to battle magical creatures that Hydra has corrupted with dark magic.
A really cool plot idea could be that the Avengers are watching Endgame in a sort of 'alternate reality cinema' where the events in the movie start to bleed into their real world. So they have to stop the movie from fully playing out to prevent chaos in their own universe. This would involve a lot of action and strategic thinking as they try to stop things like Thanos from emerging from the screen while also trying to understand the significance of what they're seeing in the movie.
Perhaps the Avengers mistake one of the Horsemen for a new super - villain. As they engage in battle, they soon realize that the Horsemen is actually after a powerful artifact that a real villain in the Avengers' world has obtained. So they form an uneasy alliance to retrieve the artifact.
Maybe in the fanfiction, the multiverse is collapsing and the Avengers of different universes are brought together by a mysterious force. They find out that an experiment gone wrong in one of the universes has caused this. So they have to travel through different universes, each with its own unique versions of the Avengers and villains. Along the way, they discover new powers and abilities that they can use to try and reverse the damage and save the multiverse.
One interesting plot could be the Avengers facing a new, super - powerful villain made of an unbreakable steel - like substance. They have to figure out how to defeat it without their usual methods working.
One interesting plot could be the Avengers facing an ancient, all - powerful cosmic entity that threatens to destroy all of existence. They have to combine their powers in ways they never thought possible, like Iron Man's technology with Thor's magic.
One idea could be the Avengers facing off against a new, powerful villain who has the ability to turn their own powers against them. This would lead to some really intense battles and strategic thinking on the Avengers' part.