Another character could be Goku from Dragon Ball. His super Saiyan powers and martial arts skills would make for an exciting dynamic with the Jetman. Goku might see the Jetman as new opponents at first, but when a greater threat emerges, they join forces. Maybe they have a competition to see who can defeat more of the enemy's minions before taking on the big bad together.
Well, if it's a crossover with Ultraman, Ultraman could be a great addition. His super strength and light - based powers would contrast well with the Jetman's abilities. They could have a friendly rivalry at first but then team up to face a powerful kaiju that is threatening both their worlds.
Alfred Pennyworth could be included. He could offer his wisdom and support to both heroes. Maybe he even has some insights about the similarities and differences between Gotham and Starling City. Another character could be Felicity Smoak. She could help with the tech - related aspects of the case they are working on together.
Characters from 'Teen Titans' could be great. Their superpowers and the Saturdays' knowledge of the supernatural could lead to some amazing adventures. Imagine Raven's magic and Beast Boy's shape - shifting working together with the Saturdays. Also, characters from 'Gargoyles' could be interesting. The Gargoyles' nocturnal nature and combat skills along with the Saturdays' would create a really unique dynamic in the fanfiction.
In a crossover with 'The Last of Us', Joel and Ellie would be great additions. Joel's survival skills and Ellie's immunity could bring new dynamics to the State of Decay world. Also, from 'Left 4 Dead', the four survivors like Bill, Francis, Zoey, and Louis could be included. Their combat skills against zombies could be interesting when combined with the State of Decay gameplay.
Joker is a must - include. His chaotic nature would add a lot of drama to any crossover. He could be causing mayhem that draws in characters from other universes or teams. Another one is Catwoman. Her ambiguous relationship with Batman can create interesting dynamics, especially when other characters are involved.
Definitely Zeref. Since he has a connection to the Etherious and also to Natsu in the original Fairy Tail story. Another good character could be Gray Fullbuster. His ice - magic could contrast well with the more chaotic and dark powers of the Etherious. Also, Mavis Vermillion could be included. Her wisdom and powerful magic could play a role in helping Natsu deal with the Etherious side of things.
Well, you could include characters from other Power Rangers series like Tommy Oliver. He has a lot of experience and different powers from various ranger forms. His presence would add a lot of depth and an interesting dynamic to the story. Also, Bulk and Skull could be added for some comic relief. They could accidentally get involved in the Jungle Fury Rangers' mission and cause some chaos in their bumbling way.
A crossover with a superhero universe like the Marvel or DC. For instance, the Jetman could cross paths with Iron Man. Tony Stark could be intrigued by the Jetman's technology and they could end up working together to upgrade their respective suits. Or perhaps they find themselves in a situation where they have to save the world from an alien invasion that targets both their dimensions.
Well, in a Naruto - One Piece crossover, characters like Luffy and Naruto would be a must. Zoro could learn some sword - based jutsu from Naruto. And Nami might be interested in the ninja tools Naruto uses for stealth and thievery prevention on the ship.
If you cross it with 'Harry Potter', you could include Harry himself. His magical abilities and his experience with the dark arts could be an interesting addition. He could interact with the Grim Tales characters, perhaps helping them with a magical problem they have in their own world.
Obviously, Merlin himself. And Arthur could be in it too. Maybe Arthur doesn't initially recognize Tiny Merlin and there are some comical misunderstandings between them.