The Duffer Brothers tread a lot of familiar ground in Stranger Things Season 2: a geeky kid and he's in mortal peril, threatened by a supernatural being from The Upside-Down; his mom erects an elaborate DIY project in her living room to help him out; the only people with any real idea about how to stop the monster are the kids who've read the Monster Manual. I did worry that perhaps the Duffer Brothers were running out of ideas already. I hope that is not the case, because overall, I really liked the sequel season, even if some of its tropes were already feeling a little tired. It would be easy to say that season 2 is a weaker version of season 1, but somehow (save for a handful of moments) it all seems to work.
What makes Stranger Things 2 really work is the villain. The “Mind Flayer” is a looming presence in the background, pulling the strings and affecting the world from afar. That the monster is some 10 story tall spider in The Upside-Down is as irrelevant as it is far from the normal physical manifestation of its namesake squid headed abomination. What is important is that it is a very real presence that looms over the protagonists and all they do. Take notes: your big bad villain need not ever be physically present to mess with and scare the characters. Your big bad villain doesn't even need to speak. But if so, how do the protagonists understand how to undermine your villain's plans and ultimately defeat them? Perhaps wisdom passed down through the ages or found in a dusty book in someone's basement. Stranger Things 2 provides much that can be mined for how to present such a threat to your PCs.