Another plot idea is that there is a multiverse - level threat that forces Spider - Man and the RWBY characters to work together. This threat could be a powerful being that is trying to merge all the universes. To stop it, they need to combine their unique powers and abilities. The RWBY characters' use of Aura and Semblances along with Spider - Man's superhuman strength and spider - sense would make for an interesting dynamic in the fight.
The plot could also involve a RWBY character going to Spider - Man's universe. Let's say Ruby ends up in New York. She'd be amazed by the skyscrapers and all the new technology. Spider - Man could help her understand his world while she tries to find a way back home. In the process, they might have to face off against some of Spider - Man's classic enemies like the Green Goblin or Doc Ock. Ruby's Crescent Rose and her combat skills would come in handy in these battles.
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 RWBY plays Spider - Man fanfiction, perhaps they'd be in a modern city setting like New York in the Spider - Man world. Ruby could be the enthusiastic leader, quickly adapting to the new powers and responsibilities. Weiss would be the one trying to keep things in order and proper. Blake would be the observant one, noticing things others miss. And Yang would be the first to jump into action when danger arises. They might face off against villains like the Green Goblin or Doctor Octopus, but with their own RWBY - style twists.
One exciting plot twist could be Spider - Man's web - slinging abilities affecting the Grimm in RWBY. Maybe his webs are able to hold the Grimm in a way that the Huntsmen and Huntresses in RWBY have never seen before. This could change the way battles are fought. Another could be that Spider - Man has to adapt to the world of Remnant, where the rules of physics and combat are different from his own world. For example, he has to figure out how to deal with Dust, the energy source in RWBY, and incorporate it into his fighting style.
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.
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.
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.
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.
Well, they could have a good laugh. Some fanfictions have really humorous takes on Spider - Man. RWBY might enjoy seeing the different interpretations of the character, his relationships, and his adventures. They could also discuss among themselves which parts they like the best and how they would change things if they were writing it.