10 Characters That Could Make Up The MCU's Thunderbolts
2. Ava Starr
Ava Starr was a complicated character during Ant-Man and the Wasp, clashing with the titular heroes on her quest to cure herself. She wasn't a villain in the traditional sense, but that doesn't mean that she wouldn't be a great asset to the team.
When we last saw her in the MCU, she had been healed to a certain degree, but required more help from Scott, Hope, Hank, and Janet. She was described by the former as a friend, but that was before the snap. When Scott returned in Endgame, understandably so, his thoughts didn't turn towards Ghost at all.
This means that Ava could be anywhere by the time Hulk snapped everyone back into existence, and could be in any state. If she has fallen further into her painful being, she could be more desperate than ever, and possibly willing to help the Thunderbolts with her unique ability in exchange for the promise of a remedy.
In the comics, Ghost was a big part of the Thunderbolts, in particular during the Dark Reign and Siege storylines, and could make a big impact on the MCU version as well.