One idea could be that Spider - Man gets transported to the DC universe through some sort of interdimensional rift. He teams up with Batman to stop a new villain who has the powers of both Green Goblin and the Joker. Their combined detective skills and combat abilities would make for an exciting story.
I think Spider - Man and Harley Quinn could be a really interesting pair. Harley's chaotic nature and unpredictable behavior would mix well with Spider - Man's sense of responsibility. They could start off as unlikely allies, with Harley initially trying to play tricks on Spider - Man but then realizing they have a common enemy and working together in a really unique way.
One idea could be that Spiderman gets transported to the DC universe due to a multiverse glitch. He teams up with Batman to stop a villain who has stolen technology from both universes. Another could be that Peter Parker goes to Metropolis for a science fair and accidentally gets involved in a battle between Superman and Lex Luthor, using his Spidey - sense and skills to help Superman.
Maybe in this fanfic, there's a multiverse crisis that causes parts of New York in the Marvel universe to merge with Gotham in the DC universe. Spiderman and Superman meet and initially have a bit of a misunderstanding due to their different ways of handling things. But then they realize they need to work together to separate the two cities again. Spiderman could use his webs to help Superman contain some of the chaos while Superman uses his strength to move large structures that are in the way.
Well, it could be really interesting. Spiderman's acrobatic fighting style and his quippy personality would be a fresh addition to the DC universe in fanfiction. He might team up with Batman, and their contrasting detective and street - level hero skills could make for some great adventures. Maybe he'd also have some run - ins with the Flash, comparing their super - speed in different ways.
There are quite a few out there. Some might focus on how Spider - Man interacts with different DC characters in a harem - like setting. For example, he could be in a world where he meets various female DC characters and forms unique relationships with them. You might find some really creative stories if you dig deep enough into the fanfiction community.
Another idea is that Greninja gets exposed to some kind of meta - human - creating substance in the DC universe and gains new powers. It could then join the Teen Titans, sharing its unique Pokémon abilities with the group. It would be interesting to see how Greninja interacts with characters like Robin, Starfire, and Cyborg, and how it uses its powers in battles against the Titans' enemies.
Definitely not. Spiderman has always been a part of the Marvel Comics universe. Marvel has its own distinct set of characters and storylines, and Spiderman is one of the most famous among them.