One interesting plot twist could be that Ultron hacks into Spider - Man's suit. This would put Spider - Man at a huge disadvantage as Ultron could control his movements or disable some of the suit's functions.
In some fanfictions, Ultron might team up with one of Spider - Man's villains, like the Green Goblin. They could create a plan to take over New York. Spider - Man would then have to face this powerful alliance. He might seek help from other superheroes he's associated with, like Iron Man or Daredevil, to combat this new threat.
One interesting plot twist could be that Venom starts to have memories of Peter Parker's life as Spider - Man. This would create a strange dynamic where Venom understands Spider - Man's motives on a deeper level and might even start to protect the things Spider - Man cares about. For example, Venom could find itself saving Mary Jane from a random mugger because it has a new - found sense of connection to Spider - Man's world.
Well, the whole Venom symbiote thing is a huge plot twist. When the alien symbiote attaches to Peter, at first it seems like a cool upgrade. But then it starts to affect his mind and personality. Eventually, Eddie Brock gets the symbiote and becomes Venom, one of Spider - Man's most iconic foes. It completely changes the dynamic in the comic world.
One exciting plot twist could be that Venom actually has a change of heart. Maybe he realizes that he and Spider - Man are both victims in a way, and they end up teaming up against a bigger threat. Another could be that Spider - Man gets infected by a different symbiote that makes him even more powerful, but also more unpredictable, and now Venom has to decide if he wants to fight this new version of Spider - Man or join him.
One interesting plot twist could be that Mega Man and Astro Boy end up teaming up instead of fighting. Maybe they realize they have a common enemy that is threatening both of their worlds. Another plot twist could be that Astro Boy discovers he has a hidden ability that makes him immune to Mega Man's weapons, which completely changes the dynamic of their fight. Or perhaps Mega Man gets corrupted by some outside force and Astro Boy has to find a way to save him and bring him back to his normal self.
A really cool plot twist could be that there is a parallel universe where Spider - Man and Ghost Rider are enemies. And in the fanfiction, elements from that universe start seeping into their world, causing confusion and making them question their alliance. This would bring in a whole new level of complexity to the story, with alternate versions of themselves causing chaos and making them fight not only external threats but also their own inner demons about who they really are.
A really interesting plot twist could be that the symbiote from the Spider - Man universe attaches itself to a major villain in My Hero Academia. This would make the villain even more powerful and unpredictable. The heroes would have to figure out how to deal with this new threat that has a combination of a quirk and the symbiote's abilities.
One possible plot twist could be that the Avengers mistake Spider - Man for an enemy at first. Maybe they see him using his powers in a way that seems suspicious. Then, as they start to fight, they realize he's just a young hero trying to do good. Another twist could be that Spider - Man has a secret connection to one of the Avengers, like he's related to Tony Stark in a way no one knew. This would add a whole new layer to their interactions.
In a Spider - Man vs Ultron fanfiction battle, Spider - Man has a good chance of winning. He's extremely agile and has his spider - sense which can help him avoid Ultron's attacks. His web - slinging also gives him an edge in mobility.
Spider - Man could use his agility. He could quickly dodge Ultron's attacks and find a weak spot in Ultron's armor. Since he's so fast and nimble, he could get in close and plant some sort of disabling device he made with his scientific knowledge.