Well, in some fanfictions, a great plot twist is when Darth Vader turns out to be an undercover agent for a greater good. He initially seems to be fighting the Avengers but then reveals his true intentions which are to stop a bigger evil that threatens both his galaxy and the Avengers' world. Also, the idea that the Avengers' technology and Darth Vader's Sith magic blend together to create a new weapon or power is really interesting. And sometimes, a plot twist can be that a character from the Star Wars universe who was thought to be dead appears in the fight between Vader and the Avengers and changes the outcome completely.
One interesting plot twist could be that Darth Vader is actually related to one of the Avengers in some way. Maybe there's a long - lost family connection that changes the whole dynamic of the fight. Another could be that the power source of the Infinity Stones somehow combines with the Force, creating a new and unexpected power that either Darth Vader or an Avenger has to control. It could also be a plot twist where the Avengers think they've defeated Vader, but he actually uses a Sith technique to possess one of them and turn the tables.
One interesting plot twist is when Darth Vader turns out to be related to a key character in the Harry Potter universe. It completely changes the way you view both universes and how they could be connected on a deeper level.
In some Batman vs Avengers fanfiction, a great plot twist is when Batman manages to hack into the Avengers' communication system and makes them fight among themselves. He then uses the chaos to his advantage. Another cool twist is that there's a greater threat looming, and Batman and the Avengers have to put aside their differences and work together. But as they do, they discover that one of the Avengers has been replaced by a shape - shifter, and Batman has to figure out who it is before it's too late. There could also be a plot twist where Batman uses a device that actually amplifies his own strength and skills to the point where he can match the Avengers' superpowers, at least temporarily.
In such a fanfic, the Avengers' diverse powers would clash with Darth Vader's formidable Force abilities. Iron Man could use his high - tech suits to try and outmaneuver Vader's lightsaber attacks. Captain America might lead the charge with his shield against Vader's dark side - enhanced combat skills. It would be an epic battle of good from different universes against Vader's Sith - influenced evil.
One idea could be a what - if scenario where Anakin in his pre - Vader state somehow gets a glimpse of his future as Vader. He could then fight against the dark side within himself that would turn him into Vader. Another could be a time - travel plot where Vader is sent back to face Anakin, and Anakin has to decide whether to accept his possible future or fight against it.
A fan fiction could also explore a parallel universe where Anakin and Darth Vader are two separate entities that co - exist. They are forced to fight not because of Anakin's fall, but due to some external force that wants to see the two most powerful Sith - like beings battle it out. This could lead to an exploration of their different fighting styles and the power dynamics between them.
A plot twist could be that Darth Vader actually reveals his true identity to Luke and Leia much earlier than in the original story. He tells them that he is their father not as a last - ditch attempt to turn Luke, but as a way to protect them from the Emperor. He then uses his knowledge of the dark side to train them in how to defend against Sith attacks. This changes the whole dynamic of their relationship and they end up forming an unlikely alliance with Vader against the greater evil of the Emperor.
The exploration of their backstories in relation to each other is very interesting. Naruto's story of growing up without parents and Darth Vader's fall from being Anakin Skywalker. In the fanfiction, it could be about how they might have made different choices if they were in each other's shoes. Also, the fanfiction might explore how the different cultures in Naruto and Star Wars, like the shinobi way and the Jedi/Sith code, could interact and influence each other.
In a Saitama vs OC fanfiction, a plot twist could be that the OC has the power to make Saitama lose his strength. However, the OC doesn't want to use this power because they admire Saitama and want to test their own strength against him fairly. Another interesting twist could be that the OC is a part of a bigger plan by some mysterious organization. They use the fight against Saitama as a distraction while they carry out their real objective elsewhere. And as the fight progresses, Saitama realizes this and has to decide whether to continue the fight or go after the real threat.
One interesting plot twist could be that Brightburn is actually from the same planet as Superman but was sent to Earth for a different purpose. Maybe he was an experiment gone wrong. Another could be that Superman's powers start to fade during the fight, making it a more even battle. Or perhaps Brightburn is being controlled by an unseen force that Superman has to figure out how to stop while also fighting him.
A really cool plot twist would be if Batman manages to steal all of Thanos' Infinity Stones and use them against him. This would completely turn the tables. Or perhaps there's a plot twist where Batman uses his detective skills to uncover a secret weakness of Thanos that no one else knew about. Maybe it has something to do with Thanos' past or his family, and Batman uses this knowledge to his advantage in the fight.