Ghost (Hannah John-Kamen) is one of the few main villains in the Avengers: Endgame were taking place.
In the comics, Ghost is primarily an Iron Man villain with a cryptic past. His real identity is a mystery, but some clues suggest he once was a talented data engineer who came up with a cutting-edge piece of tech called GhostTech, which would be used to revolutionize computer chips. However, his project was hijacked by his corporate higher-ups, who manipulated him and exploited him with no regard for his psychological well-being. This led him to fuse with his invention, gaining the ability to make himself and other objects invisible and intangible, plus the brainpower of a supercomputer. Although the MCU changed most of the character's backstory and turned him into a former SHIELD stealth operative who gained her ghost-like powers following a quantum accident, many of the original character's storylines in the comics could hint at what's coming for his cinematic counterpart.
Since Ant-Man 3 in the next few years, it's highly probable that Ghost will other MCU characters before facing the shrinking hero again.
The most popular theory that's also ed by the comics is that Hawkeye, as the archer has led the team at one point in the comics.
The question with the troubled Ava Starr isn't if but when she will resurface in the Marvel Cinematic Universe. Marvel Studios president Kevin Feige is eager to bring Ghost back some time in the future since Ant-Man & The Wasp did a great job at making her stand out from other villains as a mere victim of her circumstances. She's been lucky enough to survive inconceivable threats, so everything points at an extensive range of possibilities for her return in the ever-growing universe of Marvel movies and TV shows.
