The "Dark Phoenix" saga is one of the great triumphs of Marvel Comics. The story is a culmination of years of work from the X-Men team, providing a tale that can only exist in comic books. It’s a multi-narrative, time- and universe-spanning story that involves way more than just the main characters. It’s not a story that’s easy to adapt, but that doesn’t mean producers haven’t tried.
Dark Phoenix failed at the box office for a number of reasons, but the filmmakers faced an uphill battle from the beginning: they were trying to adapt something that almost defies a transference into a new medium. The "Dark Phoenix" story isn’t just about Jean Grey turning evil and wreaking havoc on the X-Men. It’s about a team coming into their own and doing what’s right. The story is hard to adapt into one movie - even if it's three hours long.
The "Dark Phoenix" saga was published from January to October 1980, but its origins go back to 1976 when Jean Grey was first gifted with the power of the Phoenix.
That kind of backstory is already a lot of leg work for filmgoers who either don't read comics or are casual readers at best. The MCU has gotten around the backstory problem by building an entire universe, so in order to do the "Dark Phoenix" story correctly, years of films are needed to get everyone primed for this climactic story.
Simply adapting the "Dark Phoenix" saga isn't just adapting one story. The full saga from 1980 has two main parts, both with their own multi-part narratives.
The story begins with the team searching for new mutants while Jean deals with a mysterious psychic suitor. The second part of the story is the most well-known narrative, in which Jean loses herself in the Phoenix. The final portion of the story is an outerspace battle that has its own beginning, middle, and end.
This is a kind of epilogue to the main story, but it's still necessary because it's where Phoenix sacrfices herself for the good of the universe.
The first half of the story has a plot device that's absolutely bonkers yet integral to the story. In short, Mastermind uses a device built by Emma Frost that allows him to enter Jean Grey's mind and project whatever images he wants.
Those images? A life that he constructs for Jean as a well-to-do woman in the 18th century who's in love with Mastermind's alter ego. These images serve to unlock barriers in her brain that allow Dark Phoenix to take over Jean's body and go nuts.
Before she loses herself in the guise of Dark Phoenix, Jean is controlled through the visions of herself in the past and even falls in love with Mastermind. Or at least she thinks she does.
The visions appear at the worst moments for the X-Men throughout the first half of the story, telling a story about what Jean really wants, who she is, and where her character is going. Without them, any adaptation is lacking an important part of the narrative structure.
The "Dark Phoenix" saga sees Jean Grey commit the worst atrocity imaginable when she wipes out an entire civilization without even realizing it.
In the comic, Jean beats up the X-Men after escaping from the Hellfire Club and slingshots herself around Jupiter. From there, she flies into a star and consumes it to grow more powerful.
By doing so, Jean wipes out a system of 11 planets, one of which is inhabited by “an ancient, peace-loving civilization.” Without a lot of character work, it would be hard to keep audiences on board with a maniacal mutant who eats stars.
Halfway through the story, there's a major change in both tone and style to the comic. After Jean wipes out a planet full of people, the Shi'Ar show up to put her on trial for her deeds.
By the time they arrive, she's dropped her Dark Phoenix persona and she's gone back to being sweet Jean Grey. However, that doesn't matter to the Shi'Ar, who whisk her and the X-Men away to space.
Rather than let the Shi'Ar take Jean, Professor X requests an honor battle, meaning that the X-Men have to fight the Shi'Ar in order to keep Jean on Earth. This could be an entire film unto itself.