Yellowjackets might be the creepiest show on TV right now, and it's because of how well it mixes what we do know with what we don't. We know that at some point in the high school soccer team's survivalist journey, at least one person gets eaten — likely by the very same people that she once high-fived across the soccer field after scoring a goal.
What we don't know, exactly, is who amongst the survivors did the eating/murdering, and whether that was the worst of the worst thing that happened in the woods over those fateful 19 months. Most importantly to the plane crash survivors, however, is finding out the identity of the person sending postcards reminding them of their royally messed up time in the woods.
Thus far, Natalie, Misty, Taissa, and Shauna all received postcards from this mysterious person — and it's clear that all four women have something very dark to hide about how they survived in the wilderness. While we don't know what that is exactly just yet, someone does, and they want to make sure the survivors never forget. But who could this person be, and why are they psychologically torturing these women decades after their crimes? Here are just a few ideas...
Adam
After learning that her husband is cheating on her (at least, so she thinks), Shauna started an affair with Adam, a man she met when they were involved in a minor car accident. Adam seems like a gem...which means he definitely has some shady motivations. For one thing, Adam is everywhere — including the hotel Shauna followed her husband to in order to learn of his infidelity. Coincidence? Hell no. Adam is definitely up to something, and it could be stalking Shauna and the others in order to torture them about whatever happened in the woods. If that is the case, it's possible that Adam has a secret connection to the plane crash that was thus far unknown — and his name might not even be Adam. Could he be a relative of one of the people who died (or, err, was eaten) by the girls in the wilderness?
Allie
Remember Allie, the freshman girl who broke her leg and was unable to go to Nationals with her other teammates? It's a little weird to spend so much time on a character who ends up not participating in most of the action of the show, yet many people thought it was to show how brutal Taissa could be, when push comes to shove. (She did, after all, cause her accident on the soccer field, even if she swears it was by accident.) According to Redditor Shammon5, however, there may be another reason why Allie is significant: She could be sending the postcards. It's possible that Allie had survivor's guilt over the plane crash, and only learned of what really happened to some of the Yellowjackets from someone who was in the woods much later. Perhaps Allie felt a responsibility to punish those who hurt her former teammates, as she wasn't able to protect them from harm's way.
Kevin
Natalie's former best friend is a police officer now, which could mean he has access to information that other people might not be privy to — like, say, any records about what happened to the girls after their plane crashed, and how they survived. A long shot? Sure, but Natalie seeing Kevin in a bar feels like a huge coincidence — and while she thinks she's using him in order to get information about Travis' death, it's quite possible that Kevin is really toying with her.
Taissa
One popular theory is that Taissa has a split personality or some other kind of dissociative disorder. This is potentially hinted at when she hallucinates at the party and begins seeing things that aren't there, like a deer on platter. Then there's the fact that her son has hinted at a dark presence in their house that thus far has been unexplained. At one point, Taissa's son tells her that she isn't the "bad one" when describing this unknown entity that may or may not be a figment of his imagination. If it's not his imagination, he could be referring to Taissa's other persona that's "bad." Given that Taissa was likely a part of the cannibalism, and perhaps even the leader of that human-eating tribe, it's possible that Taissa's mind split in two: Sometimes she's a vegetarian aspiring Senator, and other times she's a more monstrous figure. The later may be the one sending the postcards out of sheer guilt.
A Surprising Survivor
Right now, we don't know who made it out of the woods other than Travis, Misty, Shauna, Natalie, and Taissa — but we do know that some survivors are living off the grid. Could it be one of them sending the postcards to threaten their former friends? We have no reason to believe that anyone wants to dig up what happened in the wilderness, but the survivors would certainly be well aware that there's more to the story than the media is aware of.