Whether or not Dark Phoenix does indeed end up being the last of the main, Fox-era X-Men movies before the mutant property is absorbed into the Marvel Cinematic Universe, one thing is certain: there will be a lot of devastation. That's hardly surprising, as typically whenever Jean Grey starts glowing with orange energy, whether on the printed page or on screen, it inevitably results in a massacre. 2006's X-Men: The Last Stand, the first go at adapting the Dark Phoenix Saga resulted in several main characters being killed off, and Dark Phoenix aims to do the same. Nearly a year ago, it was rumored that one of the "First Class" era characters, i.e. someone who's been around since 2011's X-Men: First Class, will die, and a few months later, one of the first official Dark Phoenix photos showed Professor X, Cyclops, Storm and Nightcrawler together at a funeral. Now that the first Dark Phoenix trailer has been released and the footage has been studied, I suspect that Mystique is the most likely candidate to bite the dust.
In sharp contrast with Rebecca Romijn's Mystique in the original X-Men trilogy, who existed primarily just carried out Magneto's bidding, Jennifer Lawrence's Mystique in the "First Class" era has been a much more developed character. Granted, that's come at the expense of her not having much in common with her comic book counterpart, but at least it's still been interesting to follow along with her evolution. While Romijn's Mystique remained in villain territory until she was hit with that pesky mutant cure, Lawrence's iteration of the shapeshifter has been on a more complicated journey that's ultimately steered her to becoming a heroic figure, and the end of X-Men: Apocalypse saw her officially returning to the X-Men to be the new team's field commander. That's where we'll find her when we pick up with these characters nearly a decade later in Dark Phoenix, and by no means does it look like she won't have that much screen time. That being said, given her familial connection to Professor X (remember, they're foster siblings) and her complicated history with Magneto, her being killed by Jean Grey during her Phoenix freakout would certainly serve as the catalyst that drives a bigger wedge between the two men. And then there's the Beast of it all.
Unlike Mystique, who embarked on her own journey after X-Men: First Class, Beast, a.k.a. Hank McCoy, has been by Professor X's side the whole time since they first met. He's arguably been the biggest supporter for Charles Xavier's dream of mutants and humans coexisting peacefully. But as we saw in the Dark Phoenix trailer, Hank blames Charles for something goes down, and judging by the two of them wearing black suits and the shots of that funeral, I suspect this takes place after the X-Men have said goodbye to whoever it was that died. It's bad enough that we later see Beast joining up with Magneto and his allies. Let's also not forget that Mystique and Beast were once romantically involved, and while that was a long time ago (unless they picked things up again between X-Men: Apocalypse and Dark Phoenix), Beast still cares deeply about Mystique, which makes the below shot even more interesting.
Are Beast and Mystique simply having a tender moment, or is he holding her lifeless head close to his head in anguish after she's perished? I'm leaning towards the latter.
Working off all this, I'm guessing that sometime during the first half of the movie, Mystique will meet a grim end when the X-Men attempt to neutralize Jean Grey in her Phoenix form. She fits the "First Class" criteria of that rumor, and after watching her grow across four movies, her death would qualify as an emotional gut-punch. Once Mystique is dead, that kicks off the second half of Dark Phoenix, which sees Beast allying himself with Magneto to take a more aggressive approach with subduing Jean, whereas Professor X, Cyclops and their allies believe there's still the possibility they can reason with her. Which faction will be successful? That remains to be seen.
Following X-Men: Apocalypse's release, it was unclear if Jennifer Lawrence would reprise Mystique again. After all, in the years since X-Men: First Class, she's become one of Hollywood's A-list actors and won one Academy Award and three Golden Globes. It's not like she needs the X-Men franchise to further her career, and once her contract was up after Apocalypse, she could have just bid adieu. But last year, Lawrence stated that she returned for Dark Phoenix because she felt she "owed it to the fans to follow [Mystique's] journey," but I wonder if once she read the Dark Phoenix script and saw that Mystique would be killed off, that was what really pushed her to return. Dark Phoenix would give her character a proper conclusion, so if it meant putting on the blue makeup again, so be it.
Let me be clear, I don't know with 100% certainty that Mystique will die in Dark Phoenix, and even if she does meet her maker, that doesn't mean any of the other main characters won't be killed off as well later. But with Dark Phoenix looking to be more emotional than its predecessors and possibly having to wrap up this corner of the franchise, the movie needs to do a lot to stand out. Killing Mystique would certainly be shocking, but if handled correctly, it would also be meaningful and becomes one of the most memorable moments in the franchise's history. In the aftermath of X-Men: Days of Future Past, these characters were put on new life courses, so while Rebecca Romijn's Mystique made it to the 21st century, there's a good chance that Jennifer Lawrence's Mystique won't be so lucky.