Yes, that thing teased in the Dark Phoenix trailer is exactly what it looked like
[The following contains spoilers for Dark Phoenix, but if you saw the newest trailer, you’ve already been spoiled anyway.]
For the last few X-Men movies, Jennifer Lawrence has approached her role as Mystique in the same way that Harrison Ford did for Return Of The Jedi: She’s willing to do it, but she not-so-secretly thinks the character should be killed off so she doesn’t have to do it. Well, as anyone who has seen the new trailer for Dark Phoenix already knows, Jennifer Lawrence has gotten her wish. In the trailer, we see Sophie Turner’s Jean Grey sobbing in the rain about having hurt a friend, who has pointedly referred to in the past tense, and it’s cut with a sequence where Lawrence’s Mystique tries to calm Jean down as the cosmic Phoenix Force begins to take over her mind. The message is clear, even without the subsequent shot of Professor X and Beast at a funeral: Mystique is dead, and she’s been killed by Jean Grey.
In case there was still any doubt that this is the case, though, director Simon Kinberg has confirmed in a new Entertainment Weekly interview that Mystique does die. Kinberg says he wanted to make it clear from the beginning that this is “unlike other X-Men movies,” in that “people don’t just fall off buildings and dust themselves off and walk away.” He also wanted to establish just how much of a threat the Dark Phoenix is, since she’s so powerful she can kill off a big star in the trailer (not even Thanos did that).
Kinberg doesn’t address how Lawrence might feel about being killed off, but he does say say he was personally “sad about it” because he’s a fan of Lawrence’s work. In the end, though, her character is the one that makes the biggest impact by dying, since she has the strongest connection to both Professor X and Magneto. Kinberg also teased that there are other “major casualties” in the movie, even if none of them are spoiled in the trailer. Given Disney’s impending takeover of Fox assets like the X-Men rights, any one of these merry mutants could be marked for death. Jean Grey died at the end of the original Dark Phoenix Saga in the comics, but the X-Men movies in particular have never been especially faithful to the source material.