Mysterio could be a good choice too. He could use his illusions to make the homecoming a living nightmare for Spiderman and Deadpool. He could create false threats and scenarios that the two heroes have to figure out and overcome, all while trying to enjoy or at least survive the homecoming.
Green Goblin could also work well. He could be jealous of all the attention Spiderman is getting at the homecoming and decides to crash the party. His maniacal nature would contrast well with Deadpool's zany humor and Spiderman's more responsible heroism.
One possible story in a Spiderman x Deadpool Homecoming fanfic could be that Deadpool decides to crash Peter Parker's Homecoming dance. He shows up in his usual flamboyant style, causing chaos and confusion among the students. Spiderman has to both keep his identity a secret and deal with Deadpool's antics. It could be a really fun and comical take on the Homecoming event, with lots of banter between the two characters.
A good Spiderman x Deadpool Homecoming fanfic would be one that explores the emotional side of the characters. During Homecoming, Spiderman might be feeling a lot of pressure to fit in and be a normal kid while also being a superhero. Deadpool, who doesn't really have a normal life, could offer some interesting perspectives. The fanfic could show how they grow as characters through their interactions during this event, and how their relationship evolves from just being two superheroes who know each other to something deeper, like friends or even a sort of brotherly bond.
Perhaps Mister Sinister. He has always been interested in mutants like Wolverine and could see Deadpool as a useful pawn or a nuisance in his grand schemes. He might try to manipulate the situation to his advantage, causing Deadpool and Wolverine to join forces against him.
Venom could also be a main antagonist. Imagine if he somehow got enhanced and became even more powerful. He could be causing chaos in the city, and both Spiderman and Deadpool would have to figure out a way to defeat him. Deadpool's lack of fear and Spiderman's knowledge of Venom could be key factors in their fight.
One idea could be that Deadpool crashes Spiderman's homecoming dance. He shows up in his usual flamboyant style, causing chaos and hilarity. Spiderman has to try and keep Deadpool in check while also enjoying his big night. Maybe Deadpool accidentally reveals Spiderman's identity to some of the wrong people in the process.
A combination of Green Goblin and a chaos - causing creature from Equestria. The Green Goblin could team up with this creature and use his glider and bombs along with the creature's ability to spread chaos. They would target both Spider - Man's city and Twilight Sparkle's home, causing destruction and trying to assert their control.
It could be Doctor Octopus. He might team up with some evil spy organization. His mechanical arms and scientific knowledge combined with the sneaky tactics of the spies would make for a formidable foe for Spiderman and the Totally Spies.
A new character could be created specifically for this fanfic. A mad scientist who is obsessed with cross - species experiments. He sees Rachnera as a perfect specimen and wants to use her to create an army of hybrid creatures. He would target both Rachnera and Spiderman as they try to stop his evil plans.
The Kingpin could be a great antagonist. He could be trying to take over more of the city and sees Spiderman and Tigra as threats to his plans. He uses his criminal network and his physical strength to try and stop them.
The Green Goblin could be a great antagonist. His chaotic nature and advanced weaponry would pose a serious threat to both Spider - Man and She - Venom. He could be after a new power source related to the symbiote, which would bring him into conflict with our heroes.