Well, I think Hulk and Hercules might become allies. They both are incredibly strong and simple - minded in some ways. They could have a friendly competition about who is stronger, but in the end, they would realize that they have a common ground in their brute strength. Another possible pair could be Iron Man and Hephaestus. Hephaestus is the god of blacksmithing and Iron Man is a technological genius. They could exchange knowledge about creating powerful weapons and armors.
If the Avengers meet the Greek gods in fanfiction, it would be a clash of different power systems. The Avengers' powers are based on science (mostly) like Captain America's super - soldier serum or Hulk's gamma - ray - induced strength. The Greek gods, on the other hand, are more about divine power. Hercules from Greek mythology could compare his strength with the Hulk's. And Athena, the goddess of wisdom, might outwit Tony Stark in some strategic situations.
I think Klaus and Loki could be likely allies. They both have a sense of mischief and are often underestimated. They might team up to outwit their more 'righteous' counterparts. Klaus has his vampire powers and Loki has his Asgardian magic and trickery.
I think Red Hood and Hawkeye could be likely allies. They both have a certain level of street - smartness. Hawkeye is used to working in the shadows and using his skills without relying too much on superpowers, just like Red Hood.
Inuyasha and Thor could potentially be allies. They both have a sense of honor and are very powerful warriors. Thor with his hammer and Inuyasha with his sword could fight side by side against powerful enemies. Also, Captain America and Inuyasha might get along. Captain America would respect Inuyasha's fighting skills and determination, and Inuyasha would see Captain America as a worthy leader.
Iron Man. They both are very intelligent and rely on their technology a great deal. They could share ideas about improving their gadgets and suits.
Iron Man and Batman might be the most likely to clash. Iron Man is all about high - tech and showing off his latest inventions. Batman, while also using technology, is more of a brooding, solitary figure. Iron Man might see Batman as a bit of a relic or too old - fashioned in his methods. Batman, in turn, could view Iron Man as a bit too flashy and irresponsible with his power. Their egos could get in the way of them working together initially.
I think Sam from Danny Phantom would get along well with Black Widow. They both have a no - nonsense attitude and are strong - willed. Sam could teach Black Widow about environmental protection, and Black Widow could train Sam in more hand - to - hand combat skills. Also, Tucker might be an ally to Iron Man. Tucker's love for technology and his skills in that area would make him a great partner for Tony Stark. They could collaborate on creating new gadgets that combine Danny's ghostly technology with Stark's high - tech creations.
I think Sans and Iron Man could be great allies. Sans is intelligent in his own way in Glitchtale, with his knowledge of timelines and shortcuts. Iron Man is a tech genius. They could combine their knowledge to create strategies against common enemies. Iron Man might be intrigued by Sans' magic - like abilities and try to find a scientific explanation for them. Sans, on the other hand, would be impressed by Iron Man's high - tech gadgets.
Annihilus could be a likely villain. He is a powerful being from the Negative Zone. In the fanfiction, Annihilus could be drawn to Earth because of the energy signature created when the Avengers and Captain Marvel meet. He sees Earth as a prime target for conquest. His powerful cosmic control rod gives him an edge in battle. The Avengers and Captain Marvel have to quickly learn about his weaknesses and use their combined powers to stop him from destroying Earth and spreading his reign of terror across the universe.
I think Steve Rogers would be a likely ally. Steve is all about justice and doing what's right, and Castiel has a similar sense of duty in his own way. They could bond over their strong moral compasses.