Despite returning from the Upside Down in season one, Will has been unable to get rid of his connection to alternate universe. It turns out that he's being targeted by a smoke creature later named The Mind Flayer by Mike. A third of the way through the season, Will is possessed by The Mind Flayer, turning him into a spy for The Upside Down.
For the most part, Hopper and Joyce are proactive in their fight against The Upside Down. Hopper is the one who discovers the dangerous tunnels underneath Hawkins. Joyce, in her own investigation realizes that Will is drawing the creature that is attacking him and even sees it playing back a recording of Halloween night on Bob's recorder.
Far away from all the action, 11, who is living in a cabin in the woods with Hopper. We see that between Season 1 and Season 2, she escaped The Upside Down and is found by Hopper, who takes her in. 11 finds his overprotectiveness annoying and gets angry and leaves the cabin to find Mamma. In her journey, she finds her way to Chicago, where she runs into Kali. Kali is 008 from the Brenner experiments. 11 briefly joins the group of murderous vigilantes in there revenge on those who hurt them as children. Kali even helps 11 master her powers more. However, she realizes that her friends in Hawkins are in danger and goes back
While 11 was away from her friends, Max, and new girl somewhat joins the party. Dustin and Lucas are very excited to have her, but Mike does not want her. Lucas and Max grow closer, much to Dustin's dislike. The love triangle ends with Lucas and Max coming together at The Snow Ball and kissing. However, there is a great moment where Nancy dances with Dustin.
Nancy is caught in her own love triangle with Steve and Jonathan. Nancy leaves Steve to join Jonathan to seek justice for Barb. This sends them to Murray, a conspiracy theorist, who is researching Barb's disappearance. They tell him everything that happened and they record it and send them to all the news outlets. This leads to Nancy and Jonathan finally sharing their romantic moment.
All while Nancy and Jonathan are away, Steve and Dustin form a bond and team up to search for Dart, a creature that Dustin found earlier. Dart turns out to be a Demogorgon like creature that Dustin calls Demodogs. Armed with the nail bat, Steve and Dustin hunt for Dart and Dustin gets lady help and hair tips from Steve too. This leads them to meet up with Lucas and Max at the junkyard, where a pack of the creatures led by Dart attack them. Steve fights them off until they are called away by Will back to the lab.
At the lab; Bob, Mike, Joyce, Hopper, and Dr. Owens are trying to escape the lab with Will to get away from the Demodogs. Bob dies brutally after securing the escape for everyone, but Dr. Owens stays behind. He is later saved by 11 and Hopper.
The Season winds down with all roads leading back to Hawkins Lab. 11 returns to Hawkins and reunites with all her friends just in time to save them from an attack at The Byer's House. They all split up into different groups:
Joyce, Jonathan, and Nancy go to the cabin to "exorcise" Will
Mike, Dustin, Steve, Lucas, and Max fight of Billy and go to the tunnels to cause a distraction to keep the Demodogs away from the lab.
Hopper and 11 go to the lab to close the door.
The party encounter Dart in the tunnels. Dustin uses his bond with the creature and candy to "sweet talk" Dart into letting them pass.
Joyce, Nancy, and Jonathan are able to release Will from the hold of the monster by using intense heat to scare it out of him.
11 closes the door while Hopper fends off the Demodogs.
We end with The Snow Ball at school and each member getting a cute moment together, however we turn the camera to see The Upside Down and The Mind Flayer is still very much present and angry.
Joyce's moments and Ryder's portrayal is just as strong in this season.
Noah Schnapp has some phenomenal performances in this season.
The addition of Sean Astin and Paul Riser added a great 80's feel to it.
The relationship between Dustin and Steve makes this season amazing.
The threat of the "hive mind" adds a very paranoid feel to it.
Giving 11 a very "bad A" moment was cheer worthy.
The addition of Billy as the human antagonist was a great move.
Murray is a great comical addition.
The brotherly love moment that Jonathan shares with Will is nice.
Great lead into Season 3.