9) Loki
After Loki lost two of Thanos’ Infinity Stones (the Mind Stone and Tesseract) and allowed most of his Chitauri army to be destroyed by The Avengers, the Mad Titan has to want revenge against the God of Mischief. If fan theories are to be believed, that could happen in Thor: Ragnarok, but Avengers: Infinity War ultimately seems far more likely.
Seeing Loki being forced to work alongside Earth’s Mightiest Heroes would be a very interesting dynamic for the villain, though arguably something of a natural evolution after his slightly more heroic side made itself known in Thor: The Dark World.
As of right now, Tom Hiddleston seems uncertain about his future in the Marvel Cinematic Universe, but as Loki’s currently sitting on Asgard’s throne disguised as the All-Father, you have to believe he’ll factor into the two-part movies somehow.