The Kimono Girls are often overlooked. They have a connection to the Legendary Beasts in Pokemon Gold and Crystal. A fanfic could focus on their daily lives, how they came to possess their special powers related to the Legendary Beasts, and their role in protecting the balance in the Johto region. Also, the Pokedex holders in these games, like Elm's assistants, could be given more spotlight. They might have their own dreams and goals aside from just helping the professor, and a fanfic could tell their stories.
Probably the main character from the original games like Gold is quite popular. His adventures and growth as a trainer are often central in many fanfics.
Launch. She has this really interesting dual - personality thing going on. In a fanfic, she could be developed more, perhaps having her own unique fighting style related to her two personalities.
Ethan or Lyra, the main characters from the games, are always popular. You can expand on their adventures, their relationships with other trainers, and their growth as Pokemon trainers.
The Legendary Pokemon like Suicune, Raikou, and Entei can also be central characters. You could write a story about a trainer's quest to find and befriend these Legendary beasts. It could be a spiritual journey as well, as these Pokemon are often associated with certain elements and powers in the Pokemon lore.
The Prowler is a really underrated character. He has a cool look and an interesting backstory. In a fanfic, he could be a sort of anti - hero, someone who has his own code but doesn't always see eye - to - eye with Spiderman. Maybe he starts out as a foe but then they have to work together against a bigger bad.
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.
Quicksilver could be one. In the movies, he didn't get as much screen time as he could have. In a multiverse fanfiction, he could be from a universe where his powers are even more enhanced and he plays a crucial role in a team - up. Another is Mockingbird. She has great combat skills and intelligence but isn't as well - known in the Avengers context. In a multiverse story, she could be a key figure in a different reality's Avengers.
Team Rocket members are quite popular too. In fanfiction related to Pokemon Gold and Crystal, they can be portrayed in different ways. Sometimes they are more menacing and have elaborate evil plans, while other times they might have a change of heart and become allies to the protagonist. Their presence in the games provides a lot of material for fanfiction writers to play around with.
Huntress could be a great choice. She has her own sense of justice and skills that could add an interesting dynamic to the Knightfall story. Another one is Azrael. He has a complex backstory and his presence during Knightfall could be explored more deeply.
One underrated character is Black Widow. She has a wealth of spy skills and martial arts expertise. In Avengers Battleground fanfiction, she could be the one to gather intelligence on the enemies before the battle, and then use her combat skills to take out key targets during the fight. Another character is Quicksilver. His super - speed could be a game - changer on the Battleground. He could run circles around the enemies, delivering quick blows or stealing important items. And Bucky Barnes, the Winter Soldier, with his enhanced strength and combat training, could have some great storylines. Maybe he has to face off against some of his old enemies from his time as the Winter Soldier on the Battleground.