Well, there might be an OC who is a technological genius. In the Maze Runner fanfiction, this character could be using his knowledge to hack into the systems that control the Maze. For example, he might be able to find a way to temporarily disable some of the Grievers or unlock hidden passages. Thomas could then rely on this OC's skills to lead the group to safety.
There could be an OC who has a psychic connection to the Maze itself. This character, in the context of the Maze Runner fanfiction, might be able to sense when the walls are about to shift or when the Grievers are approaching even before the normal signs. Thomas, being the protagonist, would be intrigued by this OC's powers and work with them to try and find a way out of the Maze.
First, give your OC a unique backstory. Maybe they were an experiment before arriving in the Maze. Then, develop a distinct personality. For example, if they're really stubborn but also very loyal. Also, give them a special ability like being able to communicate with animals in the Maze, which can add a lot to the story.
One interesting plot idea could be a 'what if' scenario. What if Thomas and Newt got separated from the group early on in the maze? They would have to rely solely on each other for survival. Newt's knowledge of the Glade and Thomas's determination could create a really intense dynamic as they try to find their way back. They might face new and unknown threats in the maze that the others in the group haven't encountered yet.
One plot idea could be that Thomas and Teresa discover a hidden part of the maze that has a lemon tree. They realize the lemons have special properties that could help them escape. Another could be that in a memory wipe gone wrong, Teresa starts to remember a past life related to lemons and it holds the key to a mystery in the maze. Maybe they use lemons to create a signal that attracts the Creators' attention but in a way that they can bargain for their freedom.
A possible plot is that Thomas time - travels to a future version of the Maze world where everything has gone horribly wrong. He then has to bring back knowledge or an item from that future to change the present in the Maze Runner world. For example, he might find a way to defeat the Grievers once and for all in the future and has to figure out how to implement it in his own time. Or perhaps he travels to a time when the Gladers have all split up and are at war with each other, and he has to mend the relationships.
There are many interesting fanfictions about this. In some, the kiss might be a moment of sudden realization of their deep connection, perhaps in the middle of a dangerous situation in the maze. It could be a turning point in their relationship, where they finally admit their feelings for each other.
One idea could be that the OC has a special ability, like being able to communicate with the creatures in the Maze. This could change the whole dynamic of how the Gladers interact with the Maze. Another plot could be that the OC is from outside the Glade but has a connection to the people who put them there, and they struggle with whether to reveal this secret or not. Maybe the OC discovers a hidden passage in the Maze that no one else has found, leading to a whole new area full of both danger and answers.
An OC who is a natural leader but has a very different leadership style from Alby. Instead of strict rules, they focus more on building a community based on trust and friendship. This could cause some initial conflict as the Gladers are used to Alby's way, but in the long run, it could lead to new solutions for escaping the Maze.
One idea could be exploring the backstories of the characters more in - depth. For example, what was Thomas' life like before he entered the maze? Another idea is to create an alternate ending where the Gladers find a different way to escape the maze and deal with the outside world. You could also write a fanfiction about a new group of people who enter the maze after the events of the original story and how they interact with the remaining elements of the maze and any surviving Gladers.
There's also 'Teresa's True Feelings'. This fanfiction delves deep into Teresa's perspective. The kiss is a revelation for her. It shows her internal struggle with her feelings for Thomas. The story is quite detailed in exploring her character and how the kiss changes things for her in the context of the Maze Runner world.
One possible scenario in such a fanfiction could be that after they escape the maze and find a safe haven, Thomas and Teresa start a new life together. Their baby could symbolize hope for the future in the post - maze world. It might inherit their strong will and intelligence, and grow up to be a key figure in rebuilding their society.