Netflix delivered one of its most compelling stories with the sci-fi drama "Stranger Things" last year. The Duffer Brothers created a Stephen King-esque horror that paid homage to the era of the '70s and '80s, packing an innocent charm thanks largely to its coming-of-age aura. It focused on a bunch of kids in a fictional Indiana town called Hawkins, searching for their best friend, Will Byers, who was involved in a monstrous abduction and government cover-up which started unravelling to more of the townsfolk.

RELATED: Stranger Things: What Is That Monster in the Season 2 Promo?

At the heart of things was a gifted youngster, Eleven, whose special abilities due to experimentation led to the discovery of an eerie dimension known as "the Upside Down" and eventually, Will's rescue, seemingly resetting things to normal. With cryptic information on the second season now emerging and a tantalizing new trailer out, CBR decided to take a look at the dangling mysteries we want resolved in Halloween 2017!

SPOILER WARNING: Major spoilers ahead for season 1 of Stranger Things

15 WHERE DID ELEVEN GO?

Stranger-Things-Where-Did-Eleven-Go

In last season's finale, Eleven, Mike Wheeler and the boys were hiding from government authorities in the high school, but they were found after Sheriff Hopper gave her up in order to gain access to the Upside Down to rescue Will. She took out her pursuers but was severely weakened, leaving the gang to protect her. However, the blood-smelling Demogorgon came over from the dark dimension to grab the young girl due to a pre-established mental connection.

As the boys failed to ward the creature off with a slingshot a la King's "It," Eleven used her telekinesis to incapacitate the creature. She bid goodbye to her friends as she disappeared with the entity, who screamed in pain before disintegrating into ash. Hopper left Eleven's favorite food, Eggos, in the wilderness in the epilogue, leading to speculation as to where she went. All bets are that she didn't die and was transported to the Upside Down, but could her powers have evolved to teleportation? Did another monster kidnap her? Did she slip through another portal? The plot thickens.

14 WHAT IS THE UPSIDE DOWN?

Stranger-Things-Nature-of-Upside-Down

The jury's out as to the exact nature of the Upside Down. We got a more thorough tour of it in last season's finale, coincidentally titled "The Upside Down," as Hopper and Will's mother, Joyce, went to rescue him. From what we saw, it looked like a dark reflection of the real world, which begs, could it be hell? It'd be crazy if the government discovered a rift to hell, which is, of course, definitely in the '80s ballpark that clearly influences the Duffers.

If not something celestial, then from the creature's design, there are hints that the dimension could be alien, further backed by the monstrous teases we saw in the season two promo that had some fans whispering about "Cloverfield." Then there's the other argument to dispel all scientific notions behind things, and that's that it's an all-out supernatural realm or mirror universe. It would be a nice swerve for Netflix to take things into the mystical side of things, a la Limbo, from the X-Men or Mephisto's lair. Either way, we need more than a random explanation from a science teacher.

13 WILL LONNIE BYERS RETURN?

Stranger-Things-Lonnie-Byers

Lonnie Byers won the deadbeat dad of 2016. Having walked out on Joyce, leaving her to care for Will and his older brother, Jonathan, fans were shocked when he returned upon news of the boy going missing. He tricked everyone into believing that he took time off from his younger girlfriend because he truly cared about Will as it was revealed that Lonnie didn't return to find his son (whom he thought was dead), but to try to cash in on a land deal that would have seen the Byers' home sold off to a very suspicious corporation.

Joyce rightfully flipped out and booted him again, but clearly, Jonathan still loves him as we saw when he relayed the information to his dad about the boy's disappearance. However, with Will back, could Lonnie come home once more, and genuinely at that? It's not often that parents get a kid back from the dead so could Lonnie change his ways? Or will he be back to pursue that property sale? It'd definitely throw a wrench in the wheels of Hopper and Joyce's potential romance.

12 WHY DID NANCY PICK STEVE OVER JONATHAN?

Stranger-Things-Nancy-Steve

Nancy Wheeler's decision to stay with her boyfriend, Steve, over Jonathan came like a "Dawson's Creek"-style gut-punch for hopeless romantics who didn't want the nice guy to finish last. It begs the question, why not the elder Byers? Throughout the season, Steve was the stereotypical arrogant '80s teen who seemed into her for superficial reasons, and things were compounded when his jealousy built to a brutal brawl with Jonathan. This spurred Nancy on in her quest to help Jonathan find Will, knowing that he had a crush on her, which she seemed to be reciprocating behind Steve's back.

However, Steve began to show signs of sincerity, which saw him overlook the looming sense of dread in town, and team up with the duo to fight the Demogorgon at the Byers' home. This probably won him back Nancy as Jonathan clearly had a lot of family baggage to deal with, once Will was found and home again. However, after Nancy bought him back a camera to replace the one Steve broke in a hissy fit, we're eager to see how this love triangle persists.

11 ARE THERE OTHER EXPERIMENTAL PROGRAMS?

Stranger-Things-Experimental-Programs

It was revealed that Eleven's mother, Terry, was part of the experimental MKUltra program by the CIA, and that the she was taken from her pregnant mother so that her powers could be harnessed. We saw Eleven's telepathic abilities being used by Dr. Brenner to intercept information from the Russians, which eventually grew and wandered off to establish a connection with the Upside down. This was exploited by the monster who came through the gateway Eleven created.

Now, it's pretty clear here that America was trying to up their status as a global superpower and stocking up for future World Wars. Could other European and Asian countries, for example, have been conducting similar human experiments? We got a hint as to this domestic scope of experimentation, but imagine if the Russians had their test subjects spying as well, or also ending up in the Upside Down like Eleven. How are the foreigners retaliating? Maybe, their experiments weren't mental but physical, a la "Captain America." It'd be pretty cool seeing these world powers throw their superhumans at each other this season.

10 WHO IS ELEVEN'S FATHER?

Stranger-Things-Eleven-Father

Fans were left hoping that Eleven got a happy ending last season, even if it meant a reunion with the mother she never knew. Hopper's detective work and the revelations of the MKUltra program shed light on Terry's experiments, which undoubtedly helped give Eleven her powers, but one key aspect remains: who is Eleven's father and will we see him? After all, we can't rule out if he was experimented on and passed down some key genetic code, too.

The fact that the show deliberately focused on the mother could have been done to throw us off and hint at a bigger future planned for her father. What if he escaped from the program? What if Terry was mentally broken down to forget about him? What if he's just plain and normal? Either way, we figure it would up the drama factor if Eleven's father shows up looking for her now that her activities have somewhat gone public. His dynamic with Hopper, who's safeguarded the kids, would make for intriguing television and maybe it could rope Terry back in, in a more pivotal role.

9 DO OTHER FAMILIES KNOW WHAT HAPPENED?

Stranger-Things-Other-Families

We know what the Wheelers think of the entire debacle, given that Mike and Nancy fought off the Demogorgon. We know the Byers' mindset, given that they too had to fend off the creature and rescue Will from the Upside Down. However, what about the others? It's hard to believe that Dustin, Lucas and Steve's parents are still in the dark, not to mention the parents of poor Barb, who was found dead in the dark dimension.

Teens can keep a secret, perhaps, but it's very unlikely that other families are willing to keep things under wraps, knowing a repeat could occur and endanger their kids again. This PTSD may taint the other kids apart from Will and we've already read about Joyce looking for comfort in an old classmate, Bob, so the amount of details the other parents know will be crucial to the season. We can't imagine them being cool if they found out how ghastly things got a year ago. The story focused a lot on kids, but it feels like the right time to start tackling more adults.

8 DO OTHER DIMENSIONS EXIST?

Stranger-Things-Other-Dimensions

The rift we saw last season could be just one of many. We don't know how many individuals there are like Eleven, in USA or outside of it, traversing these worlds mentally. We don't know where similar programs are being run and who else stumbled upon such rifts. Some other folks may have gained access to the Upside Down like she did or some may have drifted off and opened new gateways.

The entire series would be flipped on its head if our heroes found another dimension(s), maybe even totally different from the dark one. Imagine they discovered one like, we don't know... "Pleasantville," for example. Maybe they find dimensions with other humans, or friendlier creatures or aliens, or one dealing with the afterlife, or one that has even scarier monsters waiting to be unleashed (as appears true with the tentacular monster in the preview of Season Two). The possibilities are endless because if Eleven can rupture the fabric of time and space to explore this particular dimension, if her powers evolve, there's no limit to where she can go, or who she can encounter in her journeys.

7 WHAT DEAL DID HOPPER STRIKE?

Stranger-Things-Hopper-Deal

Hopper made a sinister deal with the Department of Energy last season so he and Joyce could rescue Will. It'll be very interesting to see everyone try to contain what happened, especially as it involved selling out Eleven. The lab and rift are still in play so what's the arrangement here? Hopper and everyone in the know have a lot to keep to themselves, and it's likely that whispers and secrets will spill out into the public domain, especially with Will still not fully himself.

It's not like a deal was struck with the entire town so just what occurred that could keep Hopper from exposing the entire project? The fact that Will is back and the affiliated personnel are still keeping mum on the Upside Down is very disconcerting, but there will surely be a lot of guilt and reprisal forthcoming. Are folks getting more money? Was there a promise of more infrastructure for the town? We can't wait for juicy details on this bargain, especially with Eleven set to come back to add to the imminent Will drama.

6 DID DR. BRENNER REALLY DIE?

Stranger Things Martin Brenner

When Dr. Brenner's men were pummeled by Eleven in the finale, the blood attracted the Demogorgon, which quickly dispatched them. Brenner had finally met the monster he helped bring into this world and it lunged at him. We assumed that it killed him as it then came after the kids, but if it's one thing this series shows, we can't assume anything when it comes to death, especially off-camera ones.

Fans are wondering whether or not he died, and if so, how. After all, being a main villain, you'd think we'd be able to watch and bask in the glory of his death as he orchestrated so much pain for all these kids. Having the monster as the author of his pain was quite poetic, but we'd have loved to see it. Other theories are that maybe he was stored in the Upside Down for feeding later on. In the off-chance that he survives, we're hoping Eleven gets a chance to give him his comeuppance for tarnishing her with suffering and pain, killing off her life as Terry's daughter, Jane.

5 WHY CAN'T ANYONE PIECE TOGETHER TERRY'S STORY?

Stranger-Things-Terry-Ives

It wasn't hard for Hopper to piece together the MKUltra scandal and find out more about Terry. All it took was some simple detective work at the library. With the events that transpired and with some information hitting the news, maybe someone else could start looking at clues. If these breadcrumbs led back to Terry, it could blow the whole cover-up wide open and even lead to her wanting her daughter back.

It was a tad convenient how easily Hopper figured things out but given everything that damaged Hawkins, prying eyes are sure to emerge. If this new coalition with Hopper and the lab wanted to exist properly, then the first thing would be covering up these paper trails. Either way, there's something still odd about Terry out there in the open, as well as her family, and being able to rattle off details about an experimental program. All it takes is one or two believers to follow up on the truth out there, as Joyce also proved with Hopper.

4 WHAT IS WILL THROWING UP?

Stranger-Things-Will-Throw-Up-Slug

Fans rejoiced when Will was finally brought back from the Upside Down by Hopper and his mom, especially after we got thrown for a loop when the body double was fished out of the river. To see him survive was such a relief, but in the finale a few questions were raised. We saw him experiencing visions of the Upside Down, which could be chalked up to PTSD, but it's his throwing up slug-like creatures left fans shocked and scared.

Are they baby monsters from the Upside Down? Was this part of the plan all along? Will could well have been used for spawning purposes, which would explain why he managed to survive that sinister cocoon/incubation process in the dark dimension. It would be quite a twist if these monsters actually wanted to survive or be born into the real world so what we're seeing here may well be the first stages of spreading a pod people-type syndrome. We're eager to see what happens if they grow or attach to human hosts. Nothing says "Stranger Things" more than creatures invading, right?

3 DOES WILL KEEP HIS SLUGS SECRET?

Stranger-Things-Will-Secret

It's hard to believe he does keep this a secret, especially after his friends risked their lives to save him. Apart from his crew, Will's closeness with his family could easily point him to his mother and brother. Maybe when he meets Eleven he'd confide in her as well, but these all depend on whether he's in control of his mind and body. We don't know what effects these creatures are having inside him so we can't say if he's fully human. Maybe they've taken over Will and won't let him spill? Are these visions or is he teleporting?

It'd be interesting to see Eleven do some mind-probing on him, though, as there's a good chance she'll be able to sense any remnants of the Upside Down in him, so he won't be able to hide much. If he maintains this secret, fans could be in for a shock because, unwittingly or not, Will could be devolving into a villain, or even a monster himself. We know how close he and Mike are, so we're hoping to see their precious bond triumph in this situation.

2 WHAT ABOUT SUBJECTS 1 TO 10?

Stranger-Things-Subjects-1-10

It's obvious Eleven was a numbered subject in Dr. Brenner's program, but we are wondering what happened to her predecessors. Did they die? How far advanced were they? Did they have the same powers? If we get any backstory into how this super-army was shaping up, it would definitely shed light on the entire scope of the project in the USA. This lab feels like one of many, so if it was revealed that another set of subjects like Eleven existed (or still exist), it could blow the story wide open.

Imagine similar youthful subjects coming in and being used as enforcers in town, or to hunt down Eleven and the kids. We believe that having a darker equal to Eleven would amp the show up and intimidate us like never before. The monsters as enemies are one thing, but humans? That's a whole new relatable scare factor, especially if it's children. If the writers throw us a further bonus and show us the experimented-upon kids in foreign countries too, we'd have a better idea of the bigger, war-mongering picture at hand.

1 WHAT IS THAT NEW MONSTER?

Stranger-Things-New-Monster

Fans are already building theories that suggest "Stranger Things" is bringing us their version of the Thessalhydra next October. Like the Demogorgon, it springs from "Dungeons & Dragons," as seen when the reunited boys were playing in Mike's basement again. This creature is a reptilian acid-spewing creature akin to the hydra, with eight serpentine heads forming a ring around a large circular mouth rimmed with jagged teeth. It also has an 18-foot tail with sharp pincers.

However, the "Cloverfield" comparisons also poured in from the Superbowl spot because other fans pointed out the new creature was more a spider-like entity emerging than a hydra. It could be a dream sequence for one of the boys, but the spot teased that the "the world is turning upside down," which may mean the real world does indeed become infected to make it more like the dark dimension. This could also mean that this monster may not be the Thessalhydra itself, but one of several coming to crash the party. Does it evolve from Mike's slugs? We're curious to find out because it has that J.J. Abrams vibe!

Thoughts on our choices? Let us know what other mysteries you want solved next season!