Yes, I know that there's speculation like this all over the internet. And yes, I know I'm a few weeks late to the party. But it's fun to speculate.
So Netflix put out a season two teaser, which you've probably seen, and it's really only a series of words that sound a lot like episode titles. If you haven't seen the trailer for some reason, those titles are...
So first off - Mad Max. Well, The Road Warrior came out in 1981, so that works. But I've also read speculation that this is a new character, which I can totally buy. The kids meet someone new and christen him or her “Mad Max”.
The Boy Who Came Back to Life. This is an obvious reference to Will. A newspaper column in the last episode of season one had this exact title. Hard to glean more than that without wild speculation.
The Pumpkin Patch This, to me, sounds an awful lot like the Xenomorph pods from Aliens. And knowing how much the creators like homages, it's not a stretch at all. You saw those Alien egg looking things, didn't you?
The Palace A new place, perhaps in the Upside Down? Perhaps related to the Department of Energy facility that had been holding Eleven?
The Storm I'm guessing this is where some bigger threat emerges.
The Pollywog This makes me think very much of the Steven King book Dreamcatcher, in which a single pollywog thing can potentially spread and destroy all of mankind. Remember that weird slug-looking thing Will coughed up?
The Secret Cabin No idea.
The Brain This makes me think very much of Camazotz and The Black Thing from A Wrinkle in Time.
The Lost Brother As the finale, this has got to be significant. I'm guessing that it's a missing character who we don't yet know to be missing.
So yeah, that's a lot of speculation, much of which is likely far off base. But I felt like writing it.