The Green Goblin could be a likely villain. He has a long history with Spiderman and his maniacal nature would put him at odds with both Spiderman and Deadpool. His glider and pumpkin bombs would be a real threat to them.
It could be Orochimaru. His thirst for power and his willingness to experiment on others would put him at odds with both Naruto and Deadpool. Orochimaru might see Deadpool's regenerative abilities as something to study and Naruto as a threat to his plans. He could try to capture them and use their powers for his own dark purposes.
It could be a dark wizard who has discovered the existence of demigods and wants to use their powers for his own evil purposes. He might see Annabeth as a key to unlocking the secrets of demigod strength and try to capture her.
The Green Goblin would be really interesting. Imagine him getting his hands on a wand and trying to use magic in his own chaotic way. His maniacal laughter would echo through Hogwarts as he zooms around on his glider, causing mayhem.
Perhaps the Green Goblin could be the villain. He's a classic Spiderman foe and could pose a real threat to both Spiderman and the Shadow.
Spiderman himself could be the one to initiate an alliance. He's used to working with other heroes and he has a friendly personality. When he meets the Batfam, he would see the potential in working together and might reach out first. He would probably start with some light - hearted banter to break the ice and then suggest they team up to take on the bad guys in Gotham.
Doc Ock could also be a likely villain. He is intelligent and has those powerful mechanical arms. Imagine the two Peters trying to figure out how to stop his arms from causing destruction. MCU Peter might use his Stark - tech knowledge, while the other Peter could use his more traditional problem - solving skills to take on Doc Ock.
I believe that neither would be completely dominant in a 'deadpool meets spiderman fanfiction'. Deadpool would bring his chaos and humor, constantly trying to disrupt the normal flow. Spider - Man, on the other hand, would bring order and a sense of purpose. They would balance each other out. There might be moments where Deadpool's craziness takes over, and then there would be times when Spider - Man's leadership shines. It would be a dynamic where they both have their moments of being in control and neither has absolute dominance over the other.
Iron Man would be a likely candidate. Tony Stark is known for his sense of humor and ability to tolerate eccentric personalities. He might see Deadpool's skills and be interested in using him for certain missions, while also enjoying the banter.
I think Deadpool and Thor would be an exciting pair in the fanfiction. Thor is a noble and powerful Asgardian, while Deadpool is this crazy, regenerating anti - hero. The contrast between their personalities would be huge. Deadpool would probably make fun of Thor's old - fashioned speech and Thor would be both confused and intrigued by Deadpool's strange behavior. And in battle, they could combine Thor's lightning powers with Deadpool's unorthodox combat moves.
In a 'deadpool meets spiderman fanfiction', Deadpool could start by teasing Spider - Man about his costume. Then they could end up in a situation where they have to save the city together. Deadpool might try to steal Spider - Man's thunder during the fight, but in the end, they both come out as heroes. Spider - Man would probably be constantly trying to keep Deadpool in line, which would be really funny.