Ant-Man 3: Everything It Needs To Fix About The Franchise
3. Flesh Out Cassie Lang's Character
Given the seismic events in Avengers: Endgame, it's weird to consider how little has changed to the main players inside the Ant-Man series (mostly because they were Snap victims). Of course, the exception to this is Scott's daughter Cassie Lang, who lived out the five-year jump to be reunited with her father upon his return from the Quantum Realm.
As we already saw with Brad Davis during Spider-Man: Far From Home, five years is a long time for someone so young, where characters change drastically in both appearance and personality. Post-Endgame, Cassie would now not only be in her mid-to-late teens, but has went through the last five pivotal years without her father.
So, the film now has the task to essentially re-introduce us to her, and the easiest way to do so would be to integrate her into the Ant-Man 'team'. Through this, writers can have her trace the steps of her comic book counterpart, where she assumes the role of Stature (also setting up the possibility of her featuring in a Young Avengers somewhere down the road).
Even if they don't go down this route, expanding on her character is a golden opportunity that they would be foolish to miss out on.