3. Jocasta
Jocasta could be introduced after the Avengers sequel, initially as a villain, given that she was created by Ultron (the villain in the Avengers sequel). Ultron created Jocasta as a mate for himself whilst he was in an abandoned aerospace research center in Nassau, Long Island, New York. He based Jocasta on the mind-patterns of Wasp Hank Pym's crime-fighting partner and lover - and he set about transferring Wasp's lifeforce in to Jocasta in order to animate his robotic mate. When Jocasta learned that this would kill Wasp, she warned Wasp's allies and they managed to save her as a result which, in turn, left Jocasta as nothing more than an inanimate object. Pym took possession of her for the purposes of study and, with some tinkering, managed to revive her - and, if the tinkering was to change her personality, it could be this which brings her in to play as the primary villain in an Ant-Man movie Jocasta is a very formidable potential threat, given that he has the ability to integrate with computers, superhuman strength, durability and senses, optic cannons, the ability to generate force fields and the ability to create holographic disguises for herself - she'd be more than a handful for Pym to deal with.