A crossover with 'Stranger Things' would also be cool. The kids in Hawkins could encounter the Roswell aliens. The Roswellians' advanced technology might help the kids fight the Upside - Down monsters, or perhaps there would be some miscommunication at first due to their different worlds and concepts.
Well, in Roswell Stargate crossover fanfiction, there might be a plot where the characters from Roswell get involved in Stargate missions. Imagine the Roswell gang having to deal with the Goa'uld or the Replicators. It could also be about how the technology from Stargate affects the lives of the Roswell aliens. For instance, the Stargate could be a way for them to find a cure for their alien - related problems or a means to enhance their powers.
One idea could be that the alien technology from Roswell somehow finds its way to Smallville. The kryptonite in Smallville could have an unexpected reaction with the alien biology from Roswell. Maybe the characters from Roswell come to Smallville in search of a new energy source and end up getting involved with the local mysteries and the Kents.
Lex Luthor and Michael from Roswell would make for an exciting duo. Lex is always looking for power and knowledge, and Michael is a bit of a rebel alien. Lex might see Michael as a way to gain access to the alien technology from Roswell. Michael, on the other hand, might be suspicious of Lex but also intrigued by his resources. Their interactions would be full of tension and power plays.
One interesting idea could be a crossover with "Moana". Elsa's ice powers and Moana's connection to the ocean could create a really cool dynamic. Maybe Elsa accidentally freezes part of Moana's ocean and they have to work together to fix it. Another could be with "Tangled". Rapunzel's long hair and her adventurous spirit combined with Elsa and Anna's journey in Frozen 2 would be exciting. Rapunzel could use her hair to help them climb mountains or cross chasms. A third idea is a crossover with "Beauty and the Beast". Belle's love for books and knowledge could help Elsa understand more about her powers and the history of magic in the Frozen world.
A Thundercats and Star Wars crossover fanfiction would be really cool. The Thundercats could be in the Star Wars universe, and their unique powers and weapons could be a great addition. Maybe the Thundercats could help the Jedi or the Rebels in their fight against the Sith or the Empire. For instance, Cheetara's speed could be useful in battles, and Tygra's illusions could be used to deceive the enemy.
Max from Roswell is often a popular character in crossovers. His alien powers and leadership qualities make him interesting to incorporate into Stargate scenarios. Also, Colonel Jack O'Neill from Stargate can be a very popular choice. His military experience and sense of humor can add a lot to the Roswell - Stargate mix.
You can start by searching on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Use relevant keywords such as 'Roswell crossover' along with the name of the other fandom you're interested in. For example, if you want a crossover with 'Smallville', search 'Roswell Smallville crossover'.
A possible plot could be that there's something special about the baby because of their alien heritage. Maybe the pregnancy progresses differently compared to a normal human pregnancy. They could discover that the baby has unique powers or abilities that start to show even before it's born. This would add an element of mystery and danger as they try to protect the unborn child from those who might want to use its powers for their own gain.
A Digimon and Sailor Moon crossover is an interesting concept. The Digimon could help the Sailor Scouts in their battles against the Dark Kingdom. The magical powers of the Sailor Scouts combined with the digital powers of the Digimon would create a really unique and exciting story. And a Digimon and Avatar: The Last Airbender crossover. The Digimon could be part of the different nations, and they could use their abilities to help Aang and his friends in their quest to restore balance.
One idea could be an Atreus crossover with the world of Harry Potter. Atreus could be a new student at Hogwarts, bringing his own unique skills and knowledge from his Norse mythology background. He might struggle to adapt to the magic of the wizarding world while also showing off his own combat and survival abilities.