Spoilers for season two of Stranger Things below!
In the second season of Stranger Things, the stakes are higher. We learn that there are more people like Eleven who may very well still be out there in the world. The Upside Down has spread deep into the underbelly of Hawkins. Oh, and there's a much bigger, much scarier smoke monster that has its sights set on Hawkins.
The kids dub this monster the "Mind Flayer" after a Dungeons and Dragons creature that exhibits the same abilities. Even though Eleven closes the gate and shuts out the Mind Flayer at the end of season two, our journey with this horrible entity is far from over. We already know that season three is in early planning stages, and it's also safe to assume that the Mind Flayer will return. This conclusion mostly comes from the final shot of the season.
While all the kids pair off and have their "happily ever after" at the Hawkins Middle School Snow Ball, we flash to the Upside Down, where the monster is looming ominously over the exact same building, just in another dimension. This is all the assurance we need to know that Eleven didn't kill the monster, but simply revoked its access to our dimension. But now that it's had a taste of our reality, won't it want more?
It's not just that this beast may be more determined to see what Hawkins has to offer. This thing has also found a worthy adversary in Eleven. In a postmortem interview with The Hollywood Reporter, cocreators Matt and Ross Duffer explained how the monster reacts to Eleven: "They've shut the door on the Mind Flayer, but not only is it still there in the Upside Down, it's very much aware of the kids, and particularly Eleven. It had not encountered her and her powers until that final episode. Now, it knows that she's out there."
This curiosity could mean the Mind Flayer is especially determined to find or open another gate. Given its power, which we witness in full during the tense season finale, it's only a matter of time.
It's also worth revisiting this ominous tweet Netflix sent out way back in July, which was merely meant to promote the new season. "Some doors can't be closed," the statement read. In retrospect, this is more than just a nod to the gate Eleven accidentally opens in season one. This is a hint that, though our telekinetic heroine has shut off access, a portal between Earth and the Upside Down is almost inevitable. We may never be able to fully sever that link.