Mixing different character personalities in a unique way also helps. For example, if you cross it with Stranger Things, have the Ghost Adventures crew be both fascinated and a bit freaked out by the kids' psychic powers. And the kids could be in awe of the high - tech ghost - hunting equipment. This contrast in personalities and abilities can create a really interesting story.
You can make it unique by changing the setting. Instead of the usual spooky locations in the US, set the crossover in an ancient castle in Europe. The Ghost Adventures crew would have to deal with different types of hauntings and superstitions.
You can make it unique by changing the character dynamics. For example, make Dracula a more sympathetic character. Maybe he was cursed into his evil ways and the fanfiction could be about his journey to break the curse. Also, introduce new species or races that are not in the original Castlevania or Dracula stories. This could add new plot twists and conflicts.
You can make it unique by focusing on the character interactions. For example, if you cross it with 'Attack on Titan', instead of just having Saitama fight Titans, have him interact with the Survey Corps members on a personal level. Show how his nonchalant attitude affects them.
You can focus on character relationships. For example, if you cross Spider - Man with Iron Man, explore how Tony Stark could be a mentor figure to Peter Parker. This dynamic can add depth to the story.
To make it unique, focus on lesser - known characters. Instead of always using the main heroes like Anakin and Obi - Wan, bring in characters like Ahsoka Tano's friends from her early days in the Jedi Temple. Show their perspective during the crossover events. This will give a fresh take on the story.
Mixing the lore of both universes in a creative way. Like, if the Halo rings had an impact on the creation of the different Kingdoms in RWBY. This would not only blend the two stories but also give a fresh take on the existing RWBY lore.
To make it unique, focus on the character interactions. Don't just have the Berserk characters barge into the kingdom and start fighting. Let them form relationships, both positive and negative, with the kingdom's inhabitants. For instance, a Berserk character might fall in love with a local from the kingdom, which could change their perspective and goals.
You can start by choosing an unexpected crossover partner. For example, a crossover with Alice in Wonderland. The Major could fall into the Wonderland world and her cybernetic enhancements could be seen as strange and magical. The plot could revolve around her trying to find a way back to her own world while dealing with the illogical rules and characters of Wonderland.
Another interesting crossover could be with Buffy the Vampire Slayer. Picture the Ghost Adventures guys arriving in Sunnydale and working with Buffy to figure out the supernatural happenings there. Maybe they help Buffy with some of the ghosts she has to deal with, while she teaches them a thing or two about combatting the forces of evil.
Another way is to consider Orochimaru's snake - based abilities. In a crossover with the Mortal Kombat universe, he could be related to the race of Shokan. His snake forms could be a new type of transformation in that universe. You could also play with the idea of Orochimaru's morality in different universes. In a world like that of My Little Pony, his devious nature would stand out even more and create interesting conflicts.
Use less - known characters from both universes in the crossover. For example, instead of always using the main JoJo characters, pick some of the more obscure ones and pair them with less popular characters from the other universe you're crossing over with. This will give a fresh perspective.