Well, a really cool 'the mandalorian crossover fanfiction' concept would be a crossover with the Halo universe. The Mandalorian's combat skills and armor could be contrasted with the Spartans' abilities. Maybe they have to fight a common enemy that has invaded both their universes. Or perhaps a crossover with the Lord of the Rings. The Mandalorian could find himself in Middle - earth, having to deal with orcs and other dark forces while trying to find his way back to his own galaxy.
One idea could be a crossover with Star Wars Rebels. The Mandalorian could team up with Ezra Bridger to take on a new threat in the Outer Rim. Another idea is a crossover with the Doctor Who universe. Imagine the Mandalorian meeting the Doctor and having to deal with some time - traveling villains together.
Perhaps there could be a lost Mandalorian artifact that the Rebels accidentally discover. This draws the attention of a group of Mandalorians who think the Rebels are trying to steal it. As a result, they have to work together to figure out the true purpose of the artifact and face off against a common enemy who also wants it for their own evil plans.
One idea could be exploring the backstories of the Mandalorian warriors. For example, how they were trained and what their family lives were like before the wars.
An OC that is a young Force - sensitive foundling. The Mandalorian could take this child under his wing, and the story could explore how they both learn from each other. The OC might struggle with controlling their powers, and the Mandalorian would have to protect them from those who would seek to use the child's power for evil.
One plot idea could be Baby Yoda getting lost and the Mandalorian having to search through a dangerous planet full of strange creatures to find him. Another could be the Mandalorian teaching Baby Yoda some special skills or knowledge that is unique to his culture.
Well, a cool plot for a Star Wars Mandalorian SI fanfiction could involve the self - insert being a former Jedi in hiding. They could use their Jedi training secretly to help the Mandalorian and Grogu. Maybe they teach Grogu some new skills that are a blend of Jedi and Mandalorian ways. Also, the self - insert could have a past connection to the Sith, which adds an interesting layer of conflict as they struggle not to be drawn back to the dark side while helping the Mandalorian. Another idea is that the self - insert is an artist who uses their art to document the adventures of the Mandalorian, and in the process, their art gains some sort of magical or important significance in the Star Wars galaxy.
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.
One idea could be a story where the Mandalorian has to team up with an old enemy to fight a new, greater threat. Maybe a powerful Sith Lord emerges and they have to put aside their differences.
A Rambo crossover fanfiction could involve him crossing over into the Star Wars universe. Rambo's guerilla warfare tactics could be interesting in a galaxy far, far away. Maybe he helps the Rebel Alliance in a ground - based battle against the Empire. Or a crossover with the Predator series. Rambo would be a worthy opponent for the Predator, and the fight between them in the jungle could be epic. Also, a Rambo and John Wick crossover would be intense, two highly skilled fighters on the same side or perhaps initially at odds.
One idea could be a crossover with a modern military setting. The Decepticons could be trying to steal advanced military technology. Another is a crossover with a post - apocalyptic world where they are competing with other factions for resources. A third could be a crossover with a magical realm, with the Decepticons trying to harness the magic for their own evil purposes.
One idea could be a crossover with Naruto. Kakuzu could be sent to the Naruto universe and form an unlikely alliance with a shinobi village to fight a common enemy, like the Akatsuki from his own world turned rogue in the new universe. This would create a lot of interesting character dynamics and battles.