Donkey's dragon girlfriend could be more prominent. In fan fiction, she could have her own set of challenges that Shrek and Fiona help her with. For example, she might be having trouble fitting into the ogre - friendly world, and Shrek and Fiona could offer their support and advice.
The Riddler could be included more. He's a very interesting character with his puzzles and mind - games. In fanfiction, he could be given more complex plots and challenges for Batman and Robin to solve. Another is Catwoman. She often gets overshadowed by the more flamboyant villains. Fanfiction could explore more of her ambiguous nature and her relationship with Batman in a deeper way. Also, Commissioner Gordon. He could be more involved in the action rather than just being the one Batman reports to. He could have his own investigations parallel to Batman's in fanfiction.
One idea could be a story where Shrek and Fiona take a trip to a far - off magical land they've never been to before. They encounter new and strange creatures and have to use their wits and each other's strengths to get out of various tricky situations.
The security officers on the Enterprise during the events of The Alternative Factor are often overlooked. In fan fiction, you could give them more backstory and more significant roles. Maybe one of them has a personal vendetta against the alien entity because it reminds him of a threat from his past. Another could be a science officer who was overshadowed by the main characters in the original but has some unique insights about the alternative factor.
I think Wylie could be one. He has so much potential but often gets overshadowed by the main characters. In fan fiction, his relationship with other characters, like his family ties, could be explored more, and he could be given his own adventures that showcase his unique skills and personality.
Lady Laena Velaryon is another one. A fan fiction could explore her life more in - depth. Her relationship with her dragon, Vhagar, could be a central point. Also, her marriage to Daemon Targaryen and how she really felt about it. Maybe she had her own ambitions that were overshadowed by the events around her.
Luna Lovegood is a great choice. She has such a unique personality and view of the wizarding world. There's so much more that could be explored about her family, her beliefs, and her adventures outside of what we saw in the books. Another is Kreacher. His loyalty to the Black family and his complex relationship with Sirius could be delved into deeper.
Mantis. She has the power to manipulate emotions, which is a very interesting ability. In fan fiction, she could use this power to manipulate Thanos in a different way than what we saw in the movie. Maybe she could make him feel extreme guilt about his actions, causing him to hesitate at a crucial moment.
Brimsley is another character that could be explored more in fanfiction. He was so loyal to Queen Charlotte. A fanfiction could focus on his backstory, like how he came to serve the Queen, and his relationship with King George's staff. It could also show his unwavering loyalty during a difficult time for the royal couple, adding an interesting sub - plot.
Commander Bly. He doesn't get as much spotlight as some other clone commanders, but he has a lot of potential. His relationship with Aayla Secura could be explored more in fan fiction. Another is Barriss Offee. Before her fall, she had a lot of untapped storylines. And then there's Tiplee. She was a strong female clone commander who could be the center of some great fan - made stories.
Agent Madani is also somewhat underrated. Fanfiction could show more of her backstory and how she really feels about working in a world full of crime and violence. She could be given more complex relationships with other characters, not just Frank. For example, her interactions with other law enforcement agents or even some of the criminals she has to deal with.