Mysterio could also be a villain in this scenario. He could use his illusions to make the people of New York lose hope. Since Spider - Man has the Blue Lantern powers of hope, Mysterio would see him as a threat. He could create elaborate illusions that make it seem like the Blue Lanterns are a force of evil, causing chaos and making Spider - Man's job of spreading hope and protecting the city much more difficult.
One possible plot could be Spider - Man somehow getting his hands on a Blue Lantern ring. The Blue Lanterns are known for hope. So, Spider - Man might use the power of hope from the ring to inspire the people of New York more than ever. He could face villains like the Green Goblin or Doctor Octopus, and with the Blue Lantern powers, he'd not only fight them physically but also spread hope among the citizens, making them more resilient against the villains' threats.
Venom is also a strong candidate. In this fanfiction, he could be more powerful than ever. He might be infected with some sort of alien symbiote that gives him enhanced abilities. Venom could target Spider - Man because he wants to prove that he is the stronger one. And by attacking Spider - Man, he also draws the attention of the Avengers, which he sees as a challenge. He could start by attacking the city and luring Spider - Man and the Avengers into a trap.
Mysterio would be an interesting villain for this fanfiction. He could use the chaos of the Age of Ultron to create illusions that further disrupt the city and make it difficult for Spider - Man to tell what's real and what's not. He might also be able to trick the Avengers into believing false threats, causing internal strife within the team.
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.
It could be Doctor Doom. He might be seeking to take over multiple universes in a crossover. Spider Man stands in his way, and Doom, with his superior intellect and powerful magic, manages to defeat Spider Man. His death would then be a huge shock to other heroes in the crossover, like the Avengers or the Fantastic Four who then have to avenge him.
Loki could be a great main villain. He could trick Spider - Man into believing that Thor is a threat to Earth and set them against each other. Then, while they are fighting, Loki could carry out his real plan which might involve stealing a powerful artifact from both Asgard and Earth.
The Vulture could be a likely villain. He might see kidnapping a Spider - Man fan as a way to draw Spider - Man out into the open and then attack him when he's vulnerable trying to rescue the fan. The Vulture could be after some valuable tech that he believes Spider - Man has hidden and thinks the fan might know its location.
The Green Goblin could be a great main villain. Imagine he somehow gets hold of time - travel technology too. He could go back in time to eliminate Spider - Man before he even becomes a hero, or change events in the past to make his own power even greater in the present.
Maybe a villain who can transform into different animals. He could use this power to stalk Spider - Man in the city, changing forms to blend in and then attack when least expected. This would keep Spider - Man on his toes as he tries to figure out the pattern of the villain's attacks and how to counter this shape - shifting ability.
One interesting 'Spider Man Lantern' fanfiction could be the one where Spider Man gets the power of a Green Lantern ring. In this story, he has to learn how to use the constructs while still maintaining his acrobatic and web - slinging style. It's a great blend of two very different superhero concepts.