One interesting crossover could be the sharing of technology. For example, the warp drive from Star Trek might be compared or combined with the hyperspace technology in Babylon 5. Another aspect could be the meeting of different alien species from both universes. Maybe the Vulcans from Star Trek and the Minbari from Babylon 5 could engage in some sort of philosophical exchange.
Some fanfictions might explore how the Psi Corps in Babylon 5 would interact with the telepathic abilities in Star Trek. There could be a conflict or cooperation depending on how it's written. Also, the idea of the Federation from Star Trek and the Earth Alliance in Babylon 5 having diplomatic relations or even a trade agreement is an exciting concept in such crossovers.
Well, in some Star Trek vs Mass Effect fanfiction, there are often epic battles. Imagine the Borg from Star Trek facing off against the Reapers from Mass Effect. It would be a battle of assimilation vs destruction on a galactic scale. Also, the Starfleet officers' principles and ethics could clash or blend with the Spectres' more flexible code of conduct in Mass Effect.
Captain Kirk from Star Trek is often a popular character in these crossovers. His bold leadership style and charisma can bring a lot to the story. In Babylon 5, Sheridan is also a favorite. His ability to navigate the complex political situation in Babylon 5 can create interesting scenarios when paired with Star Trek characters.
One interesting idea could be the interaction between the different alien species from both universes. For example, seeing how Vulcans from Star Trek would interact with the Minbari from Babylon 5. Maybe they would exchange knowledge on logic and philosophy.
One interesting crossover could be the use of magic in the Star Trek universe. For example, a fanfiction might have a wizard or witch from Harry Potter end up on the Enterprise and use magic to solve some of the ship's problems, like a strange alien energy field that normal technology can't deal with.
One interesting crossover could be Kim Possible characters getting involved in a Star Trek mission. For example, Kim could use her martial arts skills to help the Star Trek crew in a physical confrontation on an alien planet. Maybe Ron Stoppable's clumsiness could lead to some comical yet ultimately helpful situations, like accidentally activating a crucial device on the Star Trek ship.
A common crossover is the appearance of Starfleet officers in the Warhammer 40k universe. They might be seen as strange and otherworldly beings. Their peaceful exploration ethos would be a sharp contrast to the constant warfare in 40k. For example, they could try to broker peace between warring factions in 40k, which would be a huge challenge given the nature of that universe.
In Star Wars vs RWBY fanfiction, an interesting aspect is the meeting of different species and races. Characters from Star Wars, like the Twi'leks or Wookiees, could interact with the humans and Faunus in RWBY. Maybe a Twi'lek could use their natural grace and charm in the RWBY world, or a Wookiee's strength could be put to use against the Grimm. Also, the concept of the Jedi and Sith aligns somewhat with the huntsmen and villains in RWBY. A Jedi - like character in RWBY might uphold the values of protecting the innocent, similar to a huntsman.
Another aspect could be the cultural exchange. Naruto's world has its own unique traditions and values, and Star's world is also full of strange and wonderful cultures. In the fanfiction, they could learn from each other's cultures. For instance, Star could introduce new forms of art and music to Naruto's village, while Naruto could teach her about the importance of loyalty and hard work within his ninja clan.
There are many cool crossovers. For instance, the concept of a Sith Lord using the dark side to control the zerg in StarCraft. The zerg's hive - mind could be influenced by the Sith's power, creating a terrifying force. Additionally, the idea of StarCraft's terran vehicles like the Siege Tank being used in a battle on a Star Wars planet, perhaps against the Empire's forces. This would bring a new level of firepower and strategy to the Star Wars battles.
One interesting crossover could be Naruto learning about the Gate of Babylon's treasures and trying to incorporate them into his jutsu. For example, he might use some of the powerful weapons from the Gate of Babylon as a way to enhance his Rasengan, creating a more powerful and unique attack. Another aspect could be a battle between Naruto and an enemy where the Gate of Babylon's abilities are pitted against Naruto's ninja skills. It would be a clash of two very different power systems, making for an exciting read.