Doc Ock could also be a great antagonist here. He could be after some new technology or power source, and Spider Man and Spider Girl get in his way. He might use his mechanical arms to try and capture them or stop them from interfering with his evil schemes. Plus, his intelligence makes him a formidable foe for the two spiders.
Maybe a new villain, created specifically for this fanfiction. This villain could have the power to manipulate time or space. He tries to use this power to reshape the city according to his own twisted vision. Spider Man and Spider Girl have to figure out how to stop him while also dealing with the chaos his power is causing in the city.
The Vulture could also be a major antagonist. His ability to fly and his sharp talons pose a great threat. Maybe he teams up with some other villains in the fanfiction to take on the two spiders at once. He could be stealing valuable items from around the city and Spider - Man and Spider - Gwen have to stop him.
Well, one possibility could be that they team up to fight a new super - villain in the city. Maybe this villain has some special powers that require both of their unique skills to defeat.
Well, it could be about them teaming up to fight a new supervillain in the city. Maybe they start off not getting along because they have different fighting styles, but then they learn from each other and become great partners.
The Kingpin could be a main antagonist. His criminal empire could pose a threat to both Spider - Man and Dazzler. He might try to use Dazzler's powers for his own gain or simply see her as a threat to his operations in the city.
One possible villain could be Doctor Octopus. He might be back with some new and improved mechanical arms, and he wants to prove that he's the superior scientist and villain by defeating both Spider Man and Spider Girl.
The Green Goblin is a common antagonist. He's always looking for ways to defeat Spider Man, and capturing him would be a big win for him. Another one is Doctor Octopus. His tentacles give him an advantage in a fight and could be used to restrain Spider Man. Venom is also a likely antagonist. His symbiotic relationship gives him enhanced strength and he might capture Spider Man to prove his superiority.
She could be an original character created by the fanfiction writer. A normal girl who just happened to be in the wrong place at the wrong time, like near a fight between Spider - Man and a villain.
They could exchange their experiences of being a superhero. Spider Man has been through a lot in his own world, and Spider Woman would have her own set of challenges. Sharing their stories could help them grow as heroes and also deepen their connection.
Often, classic Spider - Man villains like Green Goblin or Doctor Octopus can be the main antagonists. They might kidnap Mary Jane to lure Spider Man into a trap. Green Goblin, with his glider and pumpkin bombs, is always a menacing threat.
How about a new villain created specifically for the fanfiction? A being made up of the combined negative energy from all the spider - verses. This entity could be called the 'Void - Spider' and it feeds on the chaos and destruction that often follows Spider - Man in his battles. It would be a very powerful and unique threat that the Spider - Men from different universes would have to face together.