A really interesting plot twist could be that the villains from both universes are actually being controlled by a single, greater evil. For example, Queen Beryl and the Joker are being manipulated by an interdimensional being. This would force Sailor Moon and Batman to put aside their differences in fighting styles and beliefs to take on this new threat.
Another plot twist could be that Sailor Moon loses her powers and has to rely on Batman's technology and combat skills to survive. This would be a huge change for her character as she is used to relying on her magic. Meanwhile, Batman has to deal with the fact that he is now responsible for protecting someone who was once so powerful on her own.
One interesting crossover could be a story where Sailor Moon's magic and Batman's detective skills combine to solve a super - villain mystery that spans both their universes. For example, they might team up to stop a new villain who has the ability to manipulate time, a power that is of great interest in Sailor Moon's world and a threat to Batman's Gotham.
In some fanfictions, like 'The Unlikely Alliance', the plot twist is that the Hulk is actually being controlled by an unknown villain who wants to use him to take down Batman. Batman has to figure out not only how to stop the Hulk but also who is behind it all.
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 But as they do, they discover that one of the Avengers has been replaced by a shape - shifter, and Batman has to figure out who it is before it's too late.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 idea could be a time - travel scenario where Sailor Moon goes back in time to prevent a major event that led to the rise of a powerful enemy. Another could be a crossover with another popular anime, like having Sailor Moon meet Naruto and they team up to fight a new threat.
A really interesting plot twist could be that the Grimm from RWBY are somehow connected to the madness in Arkham Asylum. Maybe they are being summoned by one of the inmates who has some sort of dark magic. Another plot twist could be that a character from RWBY, like Yang, turns out to be related to one of the Arkham Asylum staff in a very unexpected way.
The cultural clash between the two universes is also fascinating. Sailor Moon's world is more about magic, friendship, and femininity, while DBZ is about fighting and male - dominated power struggles. Seeing how these two different cultures interact and influence each other in the fanfic can be really engaging. For example, Vegeta might be initially confused by the Sailor Scouts' focus on friendship as a power source.
Well, in such a fanfiction, the art styles could be blended in an interesting way. The Sailor Scouts could have a new look inspired by Batman's aesthetic, like darker colored fuku with bat - like symbols. And Batman could get a touch of Sailor Moon's magic, perhaps his utility belt having some magical items. The story could explore how two very different universes collide, and how the characters grow from the experience.
The most interesting part is the character crossovers. Seeing Goku interact with Sailor Moon or Vegeta with the Sailor Scouts brings a whole new dynamic. For example, their different fighting styles and personalities can create really engaging scenes.
One idea could be a story where a new Sailor Guardian emerges from a different dimension and has a unique power that can either help or hinder the fight against the Black Moon Clan. For example, she might be able to manipulate time in a different way than Sailor Pluto. Another plot could involve a member of the Black Moon Clan who has a change of heart and decides to secretly assist the Sailor Guardians. This would create a lot of internal conflict within the clan.