1. Will Becomes the Villain in Season Two
Something bad is happening to Will Byers. After being rescued from the Upside Down before the monster could turn him into a festering corpse a la Barb (we miss you, Barb!), little Will went back to playing Dungeons and Dragons with his crew, and eating home-cooked meals with the fam. But not so fast, bub. In one of the season's creepiest scenes, Will goes to the bathroom and pukes up a slug before transporting back to the Upside Down for a split second. Did the Demogorgon use Will to harvest its spawn? This season gave us the disappearance of Will Byers; Could the exorcism of Will Byers be next?
2. The Upside Down Was Created by Hawkins National Laboratory—on Purpose!
One of the mysteries the show failed to wrap up was how the Upside Down came to be. What is it? Perhaps it's a grand experiment by Hawkins Lab. Think about it: if an agency devoted to combatting the Soviets had access to another dimension, it would be the ultimate secret prison for spies and enemies of the state.
3. Hopper Is Actually Eleven's Father
The Duffer brothers couldn't have telegraphed this one any more than if they'd used flashing signs. While we're led to believe that El is the daughter of Terry Ives, a woman who was once subject to the tail-end of the ultra-clandestine MKUltra experiments, the season also featured a bunch of Easter eggs that have us second guessing El's true parentage. Yes, Hopper's daughter's illness gave her a bald head (just like Eleven), but he's also seen reading her Anne of Green Gables, a story about a (gasp!) 11-year-old orphan.
She eventually passed, but as we saw, the Hawkins lab is more than capable of faking the death of child. Finally, Hopper is last seen dropping off some Eggos in a box in the woods. Though the audience knows that the delicious breakfast waffles are Eleven's favorite snack, Hopper is never seen receiving that info. Lastly, and most importantly, we know the Upside Down changes people. Maybe El has become no longer recognizable to her pop.
4. Eleven Was Controlling the Monster All Along
Remember when El told Mike and co. that she's the monster? One thing's certain: El and the Demogorgon are inextricably linked. She's the one who unleashed it on the real world, and she was the only one able to destroy it. El also knew that once she killed it, she too would disappear into the ether, which is why she bid farewell to Mike just before doing the deed. Could the monster be a physical manifestation of the darkest corners of El's subconscious?
5. Barb Will Return and Seek Vengeance on All Those Who Left Her for Dead
This one's a long shot and would be total fan service from the Duffer brothers. Barb has emerged as the show's breakout star, despite appearing in only a handful of scenes. We love her disapproving parental glare, her nerdy eighties haircut, and her mom jeans from before mom jeans were cool. In other words, she deserved better than her fate as maggot food. Stranger Things: Barb's Revenge has a nice ring to it, no?