One possible plot twist could be that Pennywise actually has a fear of bats, which gives Batman an unexpected advantage. Another could be that Pennywise manages to possess Batman and uses his skills and resources to wreak havoc in Gotham, but Batman's consciousness fights back from within. Or perhaps there's a plot twist where the two form an unlikely alliance to fight a greater evil that is threatening both their existences.
In some fanfictions, the plot twist could be that it was all a simulation or a dream within a dream. Batman thinks he has killed Superman, but then realizes it was all a false reality created by some powerful entity. Or perhaps the twist is that Superman's death at Batman's hands is a necessary sacrifice to save the multiverse. Superman willingly allows Batman to kill him to prevent a greater evil from spreading across different universes.
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 But as they do, they discover that one of the Avengers has been replaced by a shape - shifter, and Batman has to figure out who it is before it's too late.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.
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.
One interesting plot twist could be that Marco, as a demon, has a hidden past connection to a powerful magic source in the Star vs the Forces of Evil universe. Maybe he was once a protector of it but got corrupted.
Perhaps the character is reborn with memories of a future event that threatens the Mikaelsons. This would put them in a position to either try to change the future or use it to their advantage within the family dynamics. They might face disbelief from the Mikaelsons at first, but as events start to unfold as they remembered, they gain more influence.
Well, in some fanfictions, a plot twist might involve the source of vengeance being misinterpreted. So, instead of the obvious villain being the target of vengeance, a new character emerges as the real cause of all the problems. This changes the whole dynamic of the vengeance and justice aspect. For example, a character might seem like a bystander but is actually pulling the strings behind the scenes, and when this is revealed, it turns the tables on who should be facing justice and who is actually in the right regarding vengeance.
A possible plot twist is that Naruto, reborn as Itachi, uses his knowledge of future events to change the Uchiha clan's fate. He could try to expose the real masterminds behind the planned Uchiha coup and prevent the massacre. This would completely change the course of the story, not just for the Uchiha but for the entire ninja world. Also, his relationship with other characters like Kakashi would be very different. Kakashi, who had a certain view of Itachi, would now be dealing with a Naruto - influenced Itachi.
In 'Frozen Bonds', the plot twist is that the Snow Queen has been manipulating events all along not for evil, but to protect Emma from a greater threat that she is unaware of. This flips the typical villain - hero perception on its head and makes for a really unique and thought - provoking story.
One possible plot twist could be a character from 'Twilight' getting superpowers like those in 'Heroes'. For example, Bella could suddenly gain the ability to fly or become invisible. This would completely change her dynamic within the 'Twilight' world and her relationship with Edward and Jacob. Another twist could be a 'Heroes' character becoming a vampire or a werewolf. It would introduce new challenges and moral dilemmas as they deal with their newfound nature.
One of the most interesting plot twists could be when a character from the original 'The Godfather' story travels back in time and accidentally changes a major event that alters the whole family's future. For example, if Michael Corleone went back and prevented his father from being shot, it would completely change the power dynamics and the family's path in the mafia world.