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.
In an 'Avengers Venom crossover fanfiction', perhaps Venom's host could be a new character related to one of the Avengers. For example, the son of Captain America who somehow gets bonded with Venom. This would create a whole new dynamic within the Avengers. The team would be conflicted between their loyalty to Cap and their fear of Venom. Meanwhile, Venom would have to learn to co - exist with the Avengers' values and not just go on a rampage.
One idea could be a Venom crossover with Spider - Man in an alternate universe where they have to team up against a common enemy like Carnage. Another could be a Venom and Deadpool crossover, with their crazy personalities clashing and then somehow working together. Maybe a Venom crossover with the X - Men, where Venom's alien nature causes some interesting reactions among the mutants.
Another interesting concept is an OC who is a scientist researching Venom's origin. They accidentally get infected and use their new powers to help the Avengers in a unique way. For example, they could have enhanced senses that allow them to detect threats before the Avengers even know they're there. They also have to struggle with the dark side of the Venom symbiote while trying to be a hero.
Perhaps Venom could cross over with the Guardians of the Galaxy. Venom's dark and edgy nature would contrast well with the Guardians' more light - hearted and space - faring adventures. They could be forced to work together to stop a powerful alien threat that is drawn to Venom's symbiote powers.
Another interesting plot could be that a mad scientist creates a device that can separate Venom from his host. However, the separation goes wrong and the symbiote energy starts to spread across the city, infecting people. Spider - Man and Venom must work together to find a way to contain the energy and save the city.
Well, a cool Venom and Spider - Man crossover fanfiction idea might be that there's a strange alien invasion. But this time, the symbiotes are being controlled by an even greater evil. Venom, having his own sense of justice, decides to work with Spider - Man. They start off not trusting each other much, but as they face the challenges, they learn to rely on one another. Also, perhaps Spider - Man has to deal with some of Venom's more violent tendencies during the fight.
I think Spider - Man would be really interesting. Since in the comics, Venom has a long history with Spider - Man, and if you bring that into the Avengers' world, it could add a whole new layer of drama. The Avengers would be caught in the middle of their relationship, not fully understanding the complex history between them.
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.