2. Willow Rosenberg (Buffy The Vampire Slayer)
If the Avengers were looking for a magic user to counter the threat of the likes of Loki, they could do a lot worse than Willow Rosenberg. Magic is definitely a weapon that the MCU Avengers are lacking and if SHIELD came to know of Willow, they would surely try to recruit her. Willow has displayed magical powers including (but not limited to) telekinesis, teleportation, magic forcefields, telepathy and energy blasts, as well as a variety of spells that require preparation which could be of great use to SHIELD and the Avengers. She's resourceful, intelligent, caring and determined and would make an excellent addition to the team which is lacking in female presence - Black Widow being the only other female Avenger. She would also find SHIELD's technology absolutely fascinating.