5) Taskmaster
Possessing the unique ability to mimic any physical movement he sees, Taskmaster became a powerful mercenary who eventually began using his skills to train other villains and their lackeys in combat. Over the years, Taskmaster has fought a variety of super-powered adversaries, many of whom are affiliated with the Avengers in some capacity.
How could a mere mortal like Taskmaster pose a serious threat to Earth’s Mightiest Heroes? Although he doesn’t possess actual powers on the level of someone like Thanos, Taskmaster has proven himself to be a serious opponent over and over against the likes of Black Panther and Captain America. His skill set includes, but is not limited to Hawkeye’s mastery of arrows, Punisher’s proficiency with firearms and the athletic ability of Daredevil.
While it wouldn’t take much for Hulk or Thor to create a Taskmaster shaped smudge on the side of a skyscraper, the writers could have a lot of fun playing him off against the mortal members of the team, such as Black Widow and Hawkeye, besting them at their own game.
Taskmaster isn’t typically associated with Thanos, but he’s been a thorn in the Avengers’ side for decades now, so he could still be utilized as an additional threat or could even act under Thanos’s direction.