The character of Dr. McCoy could bring in a different dimension. His medical expertise could be useful if the intruder has some sort of physical or mental condition. Also, his feisty personality can create some humorous and tense moments when interacting with the other characters in the context of the fanfiction.
In a 'Star Trek Turnabout Intruder Fanfic', the author might also choose to explore alternative endings. Instead of the way the episode ended, the fanfic could have Kirk and Lester finding a more amicable solution. Or perhaps the fanfic could introduce a new alien race that gets involved in the situation, adding more complexity and adventure to the story.
A more complex plot could involve time travel related to the 'Turnabout Intruder' story. The intruder could be from the future, trying to change something in the past that they believe will save their people. This would introduce a whole new layer of mystery and adventure to the fanfiction.
It's unique because it allows fans to insert their own creativity. A fanfic might introduce modern - day themes into the 'Star Trek' universe of 'Turnabout Intruder'. It could explore how contemporary social issues would be dealt with in the context of that science - fiction world. This cross - pollination of ideas makes it stand out.
Seven of Nine would be an exciting character to include. Her unique backstory and abilities could add a lot to a crossover. In a crossover with the Doctor Who universe, for instance, her Borg knowledge might be useful in dealing with the Cybermen. Picard is also a classic character. His diplomatic skills could be put to the test in a crossover with the Star Wars universe, negotiating with the Galactic Republic or the Empire.
Light Yagami from Death Note. The mind games between Light, who has the Death Note, and Jotaro with Star Platinum would be intense. Light would try to find a way to outwit Star Platinum's power while Jotaro would be trying to stop Light's plans.
Sabine Wren would be a great character to include. They have a connection in the Star Wars Rebels series, and their interactions could be further explored in fanfiction. Ezra Bridger is also a good choice. His journey and his relationship with Ashoka could be developed more. Another character could be Bo - Katan Kryze. Her Mandalorian ways and her goals could clash or align with Ashoka's, creating interesting storylines.
I think Bass would be an interesting character to add. He's a powerful and often unpredictable rival to Megaman. His presence can create a lot of conflict and tension. Also, Zero could be included. If it's set in a universe where they can cross paths, their different fighting styles and personalities could lead to some exciting interactions. Additionally, some original characters created just for the fanfiction can bring a fresh perspective to the story.
Captain Kirk is always a great choice. His leadership skills would be put to the test in a stranded situation. He could be the one making the tough decisions about resource allocation and how to deal with potential threats.
Definitely Darth Vader. His presence would create a lot of tension. He could be on a mission to hunt down the Rebels crew, and it would be a battle of wits and strength as they try to outmaneuver him.
Definitely Luke Skywalker. He could cross paths with Iden and they could have some interesting ideological battles. Leia Organa would also be a great addition. Her strong leadership and rebel spirit could contrast with Iden's Imperial upbringing. And of course, Han Solo. His roguish charm could make for some entertaining interactions with Iden.