Let's start with the Avengers. In Spider - Man's body, Jane would interact with the Avengers in a unique way. She would bring her scientific knowledge to the table, which could be very useful in some situations. However, her different personality might cause some friction. For example, Iron Man might be intrigued by the new 'Peter' but also a bit annoyed at the different approach. Captain America might see the change in 'Peter' as a sign of him growing up in a different way. On the other side, Spider - Man in Jane's body would have to deal with Asgardian friends and foes. He would befriend some of the more adventurous Asgardians, but also face the jealousy of some who don't like this 'outsider' in Jane's body. Overall, their body swap would create a lot of chaos and interesting changes in their relationships with other characters.
One interesting plot twist could be that while in Spider - Man's body, Jane discovers a new side of Peter Parker's life. She realizes the daily struggles he has in balancing his superhero duties and personal life. Maybe she accidentally reveals Spider - Man's identity to some of his enemies while trying to handle a situation in a different way than Peter would. This could lead to a whole new set of challenges for both of them as they try to fix the mess and get their bodies back.
Peter's colleagues at the Daily Bugle would find it very strange. J. Jonah Jameson would probably think it's some sort of elaborate prank by Spider - Man. He might try to expose this 'new Spider - Man' who is actually Mary Jane in his body. Mary Jane's family and friends would also be concerned about her well - being. They would try to communicate with her, but it would be difficult because she's in a different body. And Spider - Man's other friends in the superhero community might initially suspect that he's been mind - controlled or something similar, which would lead to a lot of drama and attempts to 'fix' him.
One interesting plot twist could be that while in each other's bodies, they have to deal with their respective personal relationships. Mary Jane in Spider - Man's body might struggle to handle his superhero duties and his complex relationships with villains. Meanwhile, Spider - Man in Mary Jane's body has to deal with her acting career and the pressures that come with it. Another plot twist could be that they start to understand each other on a much deeper level. Spider - Man realizes how difficult it is for Mary Jane to be constantly in the public eye and worried about his safety, and Mary Jane gains a newfound respect for the challenges he faces as a superhero.
Well, one interesting plot could be that they have to keep their identity swap a secret from their enemies. Spider - Man in the Wasp's body would have to figure out how to use her shrinking and flying abilities to fight crime, while the Wasp in Spider - Man's body would struggle with his web - slinging and enhanced strength but also use her intelligence to come up with new strategies.
In their personal lives, it would be chaos. Spider - Man has his relationships with Aunt May, Mary Jane, etc. Black Cat would have to navigate those while in his body. And Spider - Man would have to handle Black Cat's relationships with her criminal contacts. Their identities would be at risk of being exposed as they struggle to act like the other in their respective personal and superhero lives.
Perhaps a scientific experiment in Oscorp goes haywire. They could be testing some new technology related to body transfer or consciousness swapping. Black Cat and Spider - Man accidentally get caught in the experiment's field, resulting in their bodies being swapped. This would force them to adapt to each other's physical abilities very quickly.
Their relationships would change significantly. For instance, their friends might be very confused at first. Spider - Man's friends would see the Wasp acting differently in his body, and vice versa. Their romantic relationships, if any, would also be affected. They would have to explain the situation to their loved ones, and it could lead to some awkward or comical moments.
In most Spider - Man novels, Mary Jane is indeed present. She's not just a love interest but also a strong character in her own right. For example, in some novels, she has to deal with the knowledge of Peter's double life as Spider - Man. This creates interesting story arcs as she struggles with the danger that comes with loving a superhero, and also has her own life and goals that she is trying to achieve. Her presence in the novels helps to humanize Peter Parker and makes the story more than just about a superhero's adventures.
In some Spider - Man fanfictions, Mary Jane being pregnant can add a whole new layer of drama. It could mean that Spider - Man has to balance his superhero duties with being a soon - to - be father. Maybe he'll worry about protecting his family more than ever, and there could be new villains who target his unborn child or Mary Jane to get to him.