One idea could be that Tony Stark tries to modernize Dunder Mifflin's technology. He'd be frustrated by the old - fashioned ways of the office. Another could be Thor working as a temp at the office and constantly getting into comical misunderstandings because of his Asgardian ways. Maybe Hulk could be the office's security guard, scaring off any unwanted visitors in a very Hulk - like manner.
A genetic experiment gone wrong could also be a great plot for the crossover. A mad scientist tries to combine mutant and super - soldier DNA. This creates a new breed of dangerous creatures. The X - Men, with their knowledge of mutants, and the Avengers, with their combat skills and high - tech resources, must work together to contain the threat. Jean Grey's telepathic powers could be crucial in finding the source of the experiment, while Iron Man uses his technology to develop a way to reverse the genetic changes.
A cool plot could be that a new, extremely powerful mutant emerges who has the ability to control all forms of energy. This mutant's powers are so great that they start to disrupt the fabric of reality. The Avengers and the X - Men both realize that this mutant needs to be controlled or taught to manage their powers. However, different factions within both groups have different ideas on how to approach the situation. Some want to be more forceful, while others believe in a more diplomatic approach. This leads to internal conflicts within the combined group as they also battle external threats caused by the mutant's out - of - control powers.
One idea could be a crossover with 'Parks and Recreation'. The characters from 'The Office' could visit Pawnee for a government - related project. They might get into all sorts of comical situations interacting with the unique characters in 'Parks and Recreation'.
One idea could be that Merlin uses his magic to help the Avengers in a battle against a powerful magical enemy. Maybe he disguises himself as a normal human at first and then reveals his true powers when the situation is dire.
One idea could be a plot where the Avengers and DC heroes are brought together by a powerful cosmic entity that threatens both universes. They have to combine their powers and strategies to defeat it. For example, Superman and Thor could work together to take on the entity's brute strength while Batman and Iron Man figure out its weaknesses using their intellect.
One idea could be that Oliver Queen gets transported to the Avengers' universe. He could teach them some of his stealth and archery skills. Maybe he helps Hawkeye improve his arrow techniques. Another idea is that the Avengers come to Star City. They help Oliver fight a new, super - powered villain that is too much for him to handle alone. The Avengers' powers and teamwork could combine with Arrow's street - level fighting style in an interesting way.
Another interesting plot could be a sort of competition between the two groups that turns into a forced alliance. Like, both teams are after the same powerful artifact. But then they realize that a villain is also after it to destroy both their worlds. So they have to put aside their differences and work together. The Hulk could team up with Luke Cage for some brute - force action against the bad guys.
A great concept for Marvel Avengers crossover fanfiction is to have the Avengers cross paths with the Fantastic Four. The two teams could collaborate on a scientific project that goes awry, creating a new threat that only their combined powers can defeat. Another possibility is a crossover with the Eternals. Since the Eternals have been on Earth for a long time but hidden, their discovery by the Avengers could lead to a complex relationship. They might initially be at odds, but then realize they need to work together to stop a greater evil that is awakening on Earth. Also, an Avengers crossover with Blade would be interesting. Blade could seek the Avengers' help in fighting a new breed of vampires that are more powerful than ever and have ties to some dark magic that the Avengers have to figure out.
One idea could be Venom bonding with Hulk. Imagine the power boost and the chaos they could cause together. Another is Venom facing off against Thor. The contrast between Thor's godly powers and Venom's alien abilities would make for an exciting battle. Also, Venom could team up with Black Widow and use his stealth and her combat skills for some undercover missions.
Another idea is that Sherlock and Tony Stark team up. They are both highly intelligent. Tony could provide Sherlock with high - tech gadgets to aid in his investigations, while Sherlock could help Tony with his personal problems. For example, Sherlock might figure out who is trying to steal Stark Industries' secrets by observing the small details in the company's operations.