Warning: This article contains SPOILERS for Stranger Things season 3.
The Mind Flayer was always expected to return for Stranger Things season 3, and here's how it happens. Not only was the Shadow Monster teased in the final scene of season 2, but the official Stranger Things companion book revealed that the creature wasn't done with Hawkins. So how did it return and what is the creature's overall plan?
After the introduction of the Demogorgon in Stranger Things season 1, the series creators, The Duffer Brothers, took things up a notch with season 2's Shadow Monster. This monster was later referred to as the Mind Flayer, the brain from the Upside Down that used its hive mind to control its army. There was a pack of Demodogs and, of course, Will (Noah Schnapp), who served as the Mind Flayer's human host. After he was infected, the Mind Flayer gradually took over Will's mind until the monster was physically burned out of the boy.
By the end of season 2, Eleven (Millie Bobby Brown) successfully closed the Gate, seemingly trapping the Mind Flayer and killing all of its creatures in Hawkins. Viewers thought the Gate would have to be reopened for the Mind Flayer to fully return to Hawkins but that would prove not to be the case. Here's how Stranger Things explained the Mind Flayer's involvement in season 3.
How The Mind Flayer Returns In Stranger Things Season 3
The Mind Flayer didn't need to return to Hawkins because it never really left. In Stranger Things season 2, Joyce (Winona Ryder), Jonathan (Charlie Heaton), and Nancy (Natalia Dyer) took Will to Hopper's (David Harbour) remote cabin to try to burn the virus out of him. They were successful and the Mind Flayer left its host as a stream of shadowy smoke shot out of Will's body. The piece of the Mind Flayer flew through Hawkins but it was still in town when Eleven closed the Gate. The severed piece of the Shadow Monster took refuge in the Brimborn Steelworks building before it turned to dust when the Gate was closed.
The Mind Flayer's dusted appendage lays dormant until the summer of 1985 when the Russian's underground activity to open the Gate reawakens the creature. The Steelworks building becomes its official hideout. As the Gate reopens, the Mind Flayer has the control to take back the part of its body that stayed in Hawkins. Just as the Russian's Key machine starts functioning, the Mind Flayer's dusted appendage reforms and he goes back to work. This is also around the same time when the magnets stop working on Joyce's refrigerator.
The Mind Flayer Creates The Flayed - And A New Monster
To rebuild its body, the Mind Flayer lures rats into Brimborn. The hordes of infected rats turn to bubbling flesh and slithers together to form a physical body. Billy (Dacre Montgomery) becomes the Mind Flayer's first human victim in Stranger Things season 3. As he drives to meet Mrs. Wheeler (Cara Buono), he seems to hit something with his car before crashing in front of the Steelworks building. The Mind Flayer then baits him to the underground floor where Billy is attacked. He seems to make it out in one piece but instead, he has visions of the Upside Down where a group of people emerges, including a version of Billy. The Mind Flayer actually infected him by using one of its tentacles to attach to Billy's face.
The Mind Flayer then uses Billy to build up an army, which is later referred to as "the Flayed." He kidnaps Heather (Francesca Reale) the lifeguard and delivers her to the Mind Flayer who transforms her into one of the Flayed. Billy and Heather then do the same to Heather's parents. The group continues to build up the Flayed army around town until the group reaches around 30 people. Mrs. Driscoll (Peggy Miley) is also a member of the Flayed.
The monster instructs the Flayed to ingest various chemicals, as a way to make them more toxic. When the time is ready, the Mind Flayer calls back his Flayed followers and they turn to goo one by one. The goo then slithers in the same fashion of the rats and fuse with the Mind Flayer's physical body. The more people it has, the bigger and stronger it can grow. The creature then serves as the season's new version of the Mind Flayer.
The Mind Flayer's Plan Is To Kill Eleven
After the failed test with the sauna in episode 4, Max (Sadie Sink), Eleven, and the others worry about Billy's location and overall well-being as he is presumably the Mind Flayer's latest host. Eleven is able to use her powers to see that Billy is sitting in his rooms but the group agree that it must be a trap. Eleven goes to him anyway where he grabs her before she falls through his thoughts. She sees one of his childhood memories when he was with his mom at the beach. She then sees that the Mind Flayer's lair is in Brimborn Steelworks. Billy appears and says that the Flayed now know where she is and they plan to end her.
The crew eventually puts together the Mind Flayer's plan when they reunite with Hopper and Joyce in Starcourt Mall. The Mind Flayer targets Eleven because she is the only one who has the power to defeat him. Since a piece of the monster was left in Hawkins, it is able to acquire ground forces. Those forces then come together to form a new physical body so it can wreak more havoc. The Mind Flayer's intention is to kill Eleven, then her friends and family before paving the way to a new world. The Russians are unknowingly assisting in the Mind Flayer's plan to kill Eleven since they are the ones who reopen the Hawkins' Gate in the first place. Eleven holds her own in the face-off with the Mind Flayer but the bite she receives on her lower leg changes everything.
How The Mind Flayer Is Defeated In Stranger Things Season 3
The characters split up into teams to take down the new Mind Flayer monster while also closing the Gate in Hawkins. Hopper, Joyce, and Murray (Brett Gelman) travel underground to the Russian facility to take care of the Gate. They receive navigation through the underground fortress through the Scoops Troop–Dustin (Gaten Matarazzo), Steve (Joe Keery), Robin (Maya Hawke), and Erica (Priah Ferguson). Dustin is able to use his radio tower to communicate with Murray who can get Hopper and Joyce into the communications room.
Nancy and Jonathan try to get the kids out of the mall, especially Eleven since she is the main target. That plan doesn't work very well as Eleven gets left behind with Max and Mike. The monster chases Nancy's car until it realizes Eleven is still at Starcourt. Billy manages to get a hold of Eleven who can't resist because she lost her powers by draining herself and because of her wound. As Billy tries to deliver her to the Mind Flayer, her friends return and throw large fireworks at the monster as a distraction. This allows Eleven to crack Billy enough for him to come back to his true form. She uses his memory of the beach to get him to regain control of his own mind and body. Billy then stands up to the Mind Flayer and blocks its attack on Eleven before it fatally kills him.
In the meantime, Hopper and Joyce get into the communications room with the help of Dustin's acquisition of the pass code and are about to turn the keys to turn off the machine when the Russian special agent arrives. He stops them and starts a fight with Hopper that spills out of the room to where the machine is located. Time is running out but Hopper kills the man. Joyce finds a way to turn both keys on her own but if she does so, Hopper will be killed. Hopper gives her approval and she sadly turns off the machine, closing the Gate while it also seemingly sacrifices himself in the process. The Mind Flayer then collapses in the mall. With the Mind Flayer's brain severed, the body once again dies. But is the monster gone for good this time in Stranger Things?