The Avengers Are Betrayed

Regardless of whether or not Captain Marvel shows up in Avengers: Infinity War, there's really nothing to say that the Skrulls couldn't. Earth's Mightiest Heroes' plan to bring down the Mad Titan failing at the last minute would make for a devastating loss and it being revealed as the fault of one of their closest allies would serve as a real gut punch to the audience.

Picture this: we see a character like Iron Man or Black Panther is pictured having a conversation with an unknown source on a strange looking device from behind and when the camera pans around, we see that they're actually a Skrull imposter! Captain Marvelcould then expand on the concept of the shapeshifting aliens by explaining that they're under the control of the Mad Titan and that Carol Danvers has been his prisoner ever since the events of her 90s set movie. As twists go, this could work really well and sets up even bigger things to come beyond Avengers 4.