WARNING: The following article contains spoilers for Marvel’s Ant-Man and The Wasp, in theaters now.
Ant-Man and The Wasp played things differently than the average Marvel Studios film. In the 2015 original, Scott Lang faced the villainous Yellowjacket, who possessed the same power set as Ant-Man, but in the sequel the heroes are confronted by a drastically different foe. Due to a Quantum Realm-related accident that altered her physiology, Ghost has unstable molecules that permit her to become intangible, leading to exciting action sequences that mixed size-shifting and phasing.
But Ghost wasn't only set apart because of her abilities. The woman beneath the mask, Ava Starr, was transformed into a living weapon by S.H.I.E.L.D., and her constant physical pain makes her a sympathetic antagonist. She isn't evil, but rather a product of her predicament. However, once Janet van Dyne returns from the Quantum Realm and uses her newfound powers to alleviate Ava's pain, Ghost has no more reason to be an antagonist. Even the film's heroes recognize that, and they allow Ava to escape custody. Now, she doesn't have to answer to S.H.I.E.L.D., and she isn't in pain any longer. She's free to start a new path -- and it just so happens it could lead to a full-blown Thunderbolts movie.
First of all, it's important to bear in mind that while Janet uses her quantum-induced powers to alleviate Ava's pain, it appears as if it's only a temporary fix. The mid-credits scene reminds us of that, as Scott's mission is to shrink into the Quantum Realm, where he must collect a special kind of energy that will help further improve Ava's condition. As best we can tell, Ava is no longer in pain and she has more control, but it sill means she has her powers. On top of that, she still possesses her S.H.I.E.L.D. training. After all that she has done, Ava ends the film on the run with Bill Foster, looking to make amends.
Enter the Thunderbolts. In Marvel comics, they're are a team of reformed supervillains who try their hand at being superheroes. They're rougher around the edges, but they still prove heroic due to their drive for redemption. Over the years, the Thunderbolts have counted many familiar characters among their ranks; in fact, Ghost joined the ranks during Marvel's "Dark Reign" era -- and it doesn't stop there.