Perhaps there's a new criminal organization that is using both high - tech gadgets (similar to what Nightwing faces in Gotham) and genetic experiments (like those that create some of Spider - Man's foes). Nightwing and Spider - Man cross paths while investigating different aspects of this organization. They start sharing information and find out that the mastermind behind it all is planning a huge heist that would not only rob banks but also steal important scientific research. They then race against time to stop the heist and bring down the organization.
One possible plot could be that they team up to stop a powerful villain who has the ability to travel between their two cities. Maybe this villain is stealing tech from Gotham and super - powers from New York. They start off not trusting each other as they have different methods. Nightwing is more stealthy and trained in combat, while Spider - Man is more quippy and uses his webs in a very acrobatic way. But as they face challenges together, they learn to work as a team and combine their skills to take down the bad guy.
The plot might involve a multiverse - related incident. Nightwing discovers a strange anomaly in Gotham that leads him to a dimension where Spider - Man exists. Spider - Man is initially suspicious of this new figure in his city. However, they soon realize that there are forces at work trying to merge their worlds in a chaotic and dangerous way. So they have to figure out how to stop it. This could lead to some really cool action scenes, like Nightwing swinging with Spider - Man on his webs across the skyscrapers of New York.
One possible plot could be that Spider - Man gets transported to the RWBY universe. He might initially be confused by the Grimm and the Huntsmen and Huntresses. Maybe he teams up with Team RWBY to fight a new type of threat that combines the technology - based villains from his world and the Grimm from RWBY. For example, a villain could be using some sort of Dust - powered tech to create super - Grimm. Spider - Man's agility and web - slinging abilities would be a great addition to the RWBY team's combat styles.
If it's a crossover with the Fantastic Four, perhaps a cosmic entity is attacking Earth. Spider Man teams up with them to stop it. But during the battle, he's exposed to some deadly radiation from the entity. Despite the Fantastic Four's efforts to save him, his body can't withstand it, and he dies. His death could lead to the Fantastic Four creating new safety protocols for future battles.
Well, if Spider - Man meets Nightwing in a fanfiction, there could be a lot of cool things. They might team up to fight a common enemy in Gotham or New York. Maybe they start off a bit wary of each other because they come from different universes and have different ways of operating. But then they realize they can learn from each other. Spider - Man could teach Nightwing about his acrobatic web - slinging skills, and Nightwing could show Spider - Man some of his detective skills.
One possible plot could be that Spider - Man and Wonder Woman team up to stop a powerful villain who has the ability to manipulate time. Spider - Man's agility and quick thinking combined with Wonder Woman's strength and magical weapons would make for an exciting adventure. They might start off not trusting each other fully, but as they face challenges together, they learn to work as a team.
One possible plot could be that Spider - Man gets accidentally transported to the Avengers' headquarters. He has to prove himself to the Avengers at first, since they don't really know him well. Then, they discover a common enemy that is planning to attack both New York City (Spider - Man's territory) and other major cities around the world that the Avengers protect. Together, they combine their powers and skills. Spider - Man's agility and spider - sense work well with Iron Man's technology, Captain America's leadership and combat skills, Thor's godly strength, etc. They have to overcome their differences in fighting styles and strategies to defeat the enemy.
One possible plot could be that Naruto is somehow transported to the Spider - Man universe. Maybe he lands in New York and is mistaken for a new kind of super - powered being. Spider - Man, being curious, approaches him. Naruto, not understanding this new world, starts using his ninja skills which amaze the people around. They then team up to fight a common enemy like the Green Goblin who has somehow got hold of some chakra - based technology. The combination of Naruto's ninjutsu and Spider - Man's web - slinging and super strength would make for an epic battle.
One idea could be that Spider - Man somehow gets transported to the Underground in Undertale. He might initially be confused but quickly adapts his powers to the new environment. For example, he could use his webs to swing through the caverns and his spider - sense to detect approaching monsters. Maybe he teams up with Sans and Papyrus to fight against a common enemy, like a new, powerful and evil entity that threatens both the Underground and New York City in some way.
Spider - Man is a very chatty hero. He talks a lot during fights, which could be a problem for Nightwing who is more accustomed to a silent, efficient operation. But at the same time, Spider - Man's friendly nature could break through Nightwing's tough exterior. Nightwing is very loyal to his city and his cause, and Spider - Man's sense of responsibility for New York is similar. So they could bond over their shared dedication. And in a team - up, Nightwing's leadership skills could guide Spider - Man's more unruly energy, while Spider - Man's creativity could inspire Nightwing to think outside the box in combat situations.
One possible plot could be that Doctor Doom teams up with some of Spider - Man's villains like Green Goblin. The Fantastic Four and Spider - Man have to put aside their differences and work together. Spider - Man's agility and quick thinking combined with the Fantastic Four's unique powers would make for some great action scenes. For example, Spider - Man could swing in and save Sue Storm when she's in trouble, and in return, the Human Torch could help Spider - Man by burning away some of the webs that his enemies have trapped him in.
A great fanfiction idea could be that Spider - Man and Nightwing meet at a superhero convention. They both go there in civilian guise, but they sense something different about each other. Later, when trouble breaks out at the convention, they reveal their identities and work together to stop the bad guys. This would be a fun way to show their different personalities in a non - combat situation first.