The Arrow would be a great character to have a major role. His combat skills and leadership would be important in the fight against the threats from Earth X. And then there's Eobard Thawne. He has knowledge of different timelines and could use that to manipulate the events of the Crisis. Another character could be Martian Manhunter. His shape - shifting and telepathic abilities could give the heroes an edge in the battle.
Supergirl could have a major role. Her strength and powers would be very useful in the Crisis. She could be the one to lead the charge against the villains from Earth X. Also, Reverse Flash. He is always causing trouble and in a crossover, he could form an alliance with the villains of Earth X for his own gain.
Definitely Cisco Ramon. His ability to create new tech and his knowledge of the multiverse could be crucial. He could figure out ways to counter the threats from Earth X. Also, Kara Zor - El (Supergirl) again. She has the power to take on powerful foes. And don't forget about Earth X versions of the characters. For example, an evil version of Superman from Earth X could be a major antagonist, and the heroes would have to figure out how to defeat him.
A possible plot is centered around the relationships that form during the crossover. Imagine a love story between two characters from different Earths. Maybe a hero from Earth X falls in love with a hero from the main Earth. This relationship could be complicated by the differences in their worlds and the events of the Crisis. Also, a plot about the heroes having to adapt to the different rules and cultures of Earth X would be engaging.
One aspect to consider in 'Crisis on Earth X' fanfiction could be the exploration of alternate versions of characters. Writers often take advantage of the multiverse concept in this storyline to create unique character arcs that deviate from the original canon.
In 'The Flash Crisis on Earth X' fanfiction, one of the key characters is Eobard Thawne, Reverse - Flash. His complex relationship with Barry and his knowledge of time - travel can create really interesting plot twists. Also, Sara Lance, White Canary, is important. Her combat skills and her experience with the Legends of Tomorrow team bring a different dynamic to the story. And Cisco Ramon, with his ability to create and manipulate technology, is often vital in fanfictions as he can come up with solutions to various problems.
Barry Allen is quite popular. His speedster abilities can create a lot of interesting scenarios in the Crisis on Earth X setting. Writers can explore how his powers work differently on Earth X or how he teams up with alternate versions of himself.
Fanfiction often gives the opportunity to develop secondary characters more. In the context of Crisis on Earth X, these characters can play crucial roles. They might have unique skills or knowledge that help in dealing with the crisis, and their growth and contribution can be a central part of the fanfiction story.
The 'Crisis on Earth X' cartoon has a complex plot involving alternate realities and heroes fighting against a common threat. The characters include various versions of familiar superheroes with unique traits and abilities.
An Asari scientist could be a main character. She might be intrigued by the mystery of the abandoned Earth. Her knowledge of biotics and different cultures in the Mass Effect universe could help her in deciphering the secrets of Earth. She could be the one to make the first contact with any remaining humans or discover important artifacts. Also, a Krogan mercenary could be a main character. His brute strength and combat skills would be useful in exploring the dangerous and desolate Earth. He might be in it for the loot or just the thrill of adventure.
RWBY characters might initially be confused by Earthlings' lack of knowledge about Dust and Semblances. They could start by trying to educate some curious Earthlings about their world. For example, Ruby might show off her Crescent Rose to a group of engineering students, who are fascinated by its design.
Definitely Luke Skywalker. He could bring his Jedi wisdom to Earth and teach people about the Force. Han Solo would also be great. His roguish charm would be fun to see on Earth. And of course, Darth Vader. His imposing presence would create a lot of drama.
Gollum could be an interesting addition to a crossover. His split personality and knowledge of the Ring could add a lot of depth. If crossed with a story like Alice in Wonderland, Gollum could be lured by the idea of some 'precious' object in Wonderland and his journey to find it could be a wild and unpredictable adventure.