The plot might involve the Avengers being called to investigate strange energy signatures which turn out to be related to the AllSpark from the Transformers universe. The Decepticons are after the AllSpark and the Autobots are trying to protect it. The Avengers and Autobots join forces. Thor could use his powers to fight off the Decepticons' attacks from the air, while Hulk could take on the physically strong ones. The fanfiction could also explore how the different personalities of the Avengers and Transformers interact, like the witty banter between Spider - Man and Bumblebee.
Well, perhaps a plot where the AllSpark from Transformers ends up on Earth and its energy attracts both the Transformers and the Avengers. The Avengers are initially suspicious of the Transformers. But as they learn about the Decepticons' plan to use the AllSpark for evil, they join forces. The Hulk could even have some interesting interactions with the larger Transformers like Grimlock.
A great plot could be that a powerful artifact from the Transformers universe is found on Earth and it has the power to either save or destroy the planet. The Avengers initially think it's a new weapon or power source, while the Autobots know its true origin. They have to convince the Avengers of its importance and together protect it from the Decepticons and any other villains who want to use it for their own evil purposes.
Optimus Prime and Captain America would be really interesting. They are both natural leaders, with a strong sense of justice. Optimus is a noble leader of the Autobots, and Captain America is the moral compass of the Avengers. They could share their leadership experiences and strategies.
I think Spider - Man and Bumblebee would have really fun interactions. Spider - Man is known for his quick - witted remarks and Bumblebee, with his beeps and boops that can be translated into humorous comments. Captain America and Ultra Magnus could also have an interesting dynamic. Cap's old - fashioned values of honor and duty could be contrasted and yet find common ground with Ultra Magnus' strict sense of Autobot law and order.
Optimus Prime and Thor would be a really interesting pairing. They are both noble leaders. Optimus with his wisdom and strength, and Thor with his godly powers. They could exchange ideas about leadership and honor while fighting side by side against powerful foes. Their weapons are also quite interesting to compare - Optimus' ion blaster and Thor's hammer.
One common theme is the clash of different technologies. The high - tech world of the Avengers with Iron Man's suits and SHIELD's gadgets, and the advanced alien technology of the Transformers. Another theme is teamwork. How the Avengers, who are used to working together, interact with the Autobots or Decepticons, which have their own group dynamics.
In a Transformers and Bumblebee crossover fanfiction, Bumblebee could lose his memory and the other Transformers have to help him regain it while also protecting him from the Decepticons who see this as an opportunity to take him out. They go on a journey through different planets and encounter various strange species along the way.
In a world where the Transformers and Megatron's universe collide, Optimus Prime finds himself in an unfamiliar realm. He discovers Megatron has formed an unlikely alliance with a group of humans. Optimus is initially skeptical but realizes they must work together to face a new common enemy, a powerful energy - sucking creature from another dimension. The story unfolds as they learn to trust each other and combine their strengths.
One idea could be that Anastasia is a long - lost Cybertronian in human form. The Autobots discover her true identity while on Earth and have to protect her from the Decepticons who want to use her unique connection to both Earth and Cybertron for their evil plans.