4. Tigra
Though this character would perhaps suit the current Avengers universe in her original, non-super powered crime fighting role as The Cat, Greer Grant Nelson is a woman who mutated into the super powered half tiger, half woman Tigra after asking her old physics professor to let her undergo treatments that would give her special abilities. After being wounded by Hydra, she is later revived by a magical humanoid race known as the Cat People (which themselves where created by sorcery during the dark ages), who are powerful scientists and sorcerers who have created a process which combines science, magic and mental powers to turn any human woman into a half tiger hybrid with greatly enhanced powers including super speed, retractable claws and superhuman strength. The fact that the character would look ridiculous and would be laughable up against the other Avengers (especially the only current female Black Widow) isnt the only reason to exclude this from sequel. Not only would the backstory be difficult to effectively convey in a movie (by no means impossible), Batman already has a VERY popular superhero female in Catwoman. Added to the fact that it is not out of the realms of reality that we could very well see a Black Cat (from the Spider-Man comics) appear in a Spider-Man sequel anytime soon (already having had been cast in cancelled the Spider-man 4, coincidentally the role was given to Anne Hathaway) putting one of very few female superheroes in The Avengers who is also a cat would be considered by many as very lazy and unoriginal. Again, the same applies to The Avenger Hellcat, Tigras apprentice.