Daisy Johnson from Agents of SHIELD and Oliver Queen from Arrow would also be an interesting duo. Daisy has her Inhuman powers and combat skills, while Oliver is an expert archer and martial artist. They could fight side - side in a big battle against a powerful villain.
Sasuke and Grant Ward would be an interesting pair. Sasuke has his dark past and his thirst for power, and Ward also has a complex and somewhat dark past. They could either become rivals, constantly trying to outdo each other in terms of combat skills and power, or they could find some common ground and work together in a strange way, like using Sasuke's Sharingan and Ward's combat training to take on a powerful enemy.
Definitely Harry Potter and Daisy Johnson. Harry has his magic skills and experience in fighting dark wizards, while Daisy has her Inhuman powers and combat training. They could learn a lot from each other. Harry could teach Daisy about different magical spells and Daisy could show Harry some of her cool combat moves. Their personalities are also quite different but in a way that could lead to great character development and an interesting dynamic in the story.
Definitely Captain America and Agent Coulson. Captain America represents the old - school heroism of the Avengers and Coulson is the heart and soul of Agents of Shield. Their different leadership styles and moral compasses would create a great dynamic. They could learn from each other, like Coulson teaching Cap about modern technology and Cap teaching Coulson about the values of the past.
I think Natasha Romanoff and Melinda May would be an interesting pair. Both are strong, badass women with a lot of combat experience. They could share their stories of their past missions, and also train together. Maybe they could even have a friendly competition to see who is better at hand - to - hand combat or espionage.
I think Daisy Johnson would be really interesting. She has her unique powers and a complex backstory from her time in SHIELD. In a crossover, she could interact with the likes of Thor. Maybe she could learn some new ways to control her powers from him, as he has experience with his own godly powers. And she could also show the Avengers her skills in combat and stealth that she learned in SHIELD. It would be fascinating to see how she holds her own among the super - powerful Avengers.
Another interesting pairing could be Batman and Daisy Johnson. Daisy has her inhuman powers, especially her seismic abilities. Batman could be intrigued by her powers and try to find ways to use them effectively in combat. And Daisy could learn a lot from Batman's combat training and his no - nonsense attitude towards fighting crime. They could form a strong duo when it comes to facing enemies that require both brute force and strategic thinking.
Daisy Johnson from Agents of Shield would be really interesting. Her own Inhuman powers make her a natural bridge between the two groups. She could help the Inhumans understand the ways of Shield and vice versa. Also, Black Bolt from the Inhumans is fascinating. His power is so extreme that just speaking could cause destruction. How would he interact with the Agents of Shield? What kind of strategies would they have to come up with to communicate with him? It would be really engaging to explore.
One really interesting character pairing could be Fitz - Simmons and the TMNT as a whole. Fitz - Simmons are brilliant scientists, and the turtles are a scientific anomaly. They could study the turtles and their mutagenic origin. The turtles could also benefit from Fitz - Simmons' knowledge of advanced technology. Another pairing that would be cool is Agent Ward (assuming he's not evil in this fanfiction) and Leonardo. Ward is a skilled agent, and Leonardo is a skilled ninja. They could exchange fighting and survival skills, and their different perspectives on loyalty and duty could lead to some interesting story arcs.
I think the interaction between Coulson and Captain America would be really interesting. Coulson is a big fan of Captain America, and Steve would be impressed by Coulson's leadership and the way he holds his team together. They could exchange stories about their different experiences in the war - Steve from World War II and Coulson from more modern conflicts.
Sonic and Pikachu would be a really interesting pair. Sonic's high - speed and adventurous nature combined with Pikachu's electric powers and cute but brave personality could lead to some really fun and action - packed scenes. They could race each other and then work together to face challenges.