Maybe a foreign exchange student who has her own set of martial arts skills. She could initially be a bit of an enigma to Spider - Man, but later they team up to fight crime. She could bring a new fighting style and a different perspective to the story.
A character like a wise old hermit living in Central Park who has some ancient knowledge about a powerful artifact. Spider - Man discovers this hermit during one of his patrols, and the hermit's knowledge ends up being crucial in a battle against a powerful, ancient - themed villain.
A new character could be a young inventor who idolizes Spider - Man. This character could accidentally create a device that has the potential to be very dangerous in the wrong hands, and Spider - Man has to help him keep it safe.
A new character could be a tech - savvy girl who discovers Peter's identity and offers to be his 'Q' of sorts. She helps him upgrade his suit and gives him new gadgets to fight crime with.
The Green Goblin could be a great main villain in a crossover. Imagine if he teams up with Doctor Doom from the Fantastic Four universe. Their combined evil intelligence and power would be a huge threat to Spider - Man and whoever he teams up with in the crossover.
One underrated character is Robbie Robertson. He could be given a more central role in a fanfiction. Maybe he discovers some shady business going on in the city that is related to the villains Spider - Man faces. He could then team up with Spider - Man to expose the truth. Another underrated character is Betty Brant. She could be developed more as a strong - willed journalist who is trying to break big stories, and her relationship with Peter Parker could be explored in a different way.
It could be a character like the Hobgoblin. He's a classic Spider - Man villain and would bring a lot of chaos to the story.
A character with the power to manipulate time within the Spider - Verse could be really interesting. This character could accidentally disrupt the normal flow of time in different universes while trying to save their own universe from destruction. It would create a whole new set of challenges for Spider - Man and his allies as they try to restore order.
Perhaps a new character, like a genetically - engineered super - soldier gone wrong. This villain could have super strength and agility similar to Spider - Man, but with a more aggressive and unpredictable nature. He might see Spider - Man as a rival and be determined to prove that he is the superior one in the city.
It could be a mad scientist who creates mutated creatures to cause chaos in the city.
A new character that could be interesting is a scientist who was working on a project to reverse the effects of the symbiote. This character could have a complex backstory, like they were once a student of Dr. Connors and turned to this research after seeing the chaos the symbiote brought.
Perhaps Doctor Octopus. Knowing who Spider - Man really is, he might use his intelligence and his mechanical arms to create elaborate traps for Peter Parker at his home or workplace. He could also try to expose Spider - Man's secrets further to the public and turn the public against him.
One great fanfiction could be about Spider - Man joining the Avengers for a mission against a powerful new villain. In this story, Spider - Man's unique abilities like his agility and web - slinging would add a new dynamic to the Avengers' combat strategy. Maybe he helps Iron Man with some technical glitches during the fight while also using his street - smart skills to gather intel. Another interesting crossover could be a story where Spider - Man has to train some of the newer Avengers members, like Scarlet Witch. His experience as a solo hero in the streets of New York gives him a different perspective on heroism compared to the more global - scale Avengers.