My Stranger Things Theory: Mike made up everything past season 1
Ok so just like hear me out.
Everything and I do mean everything that happened in season 1 was very real and did happen, Will's disappearance, the Demogorgon, Elven, all of it except the ending. Noone's sure what exactly happened to El but she disintegrated so she's probs dead, but Will is entirely dead when Joyce and Hopper went to save him they found and recovered his body.
Each member of the party grieved in their own way but Mike was being weird, he kept talking to himself and insisting that will is still alive when asked where Will is Mike kept saying "At a doctors appointment."
When the anniversary of Mike's disappearance rolls around Mike starts getting worse, talking to "Will" more and more and then he starts saying that El is alive and hopper has her in his cabin, when asked Hopper said "I don't have a cabin." and he wasn't lying.
Everything that happened with Nancy in season 2 was real, she wanted justice for Bard after all and Johnathan wanted justice for will. Nancy and Johnathan asked Steve, who was still with Nancy at this point, to watch over the kids keep em safe. The boys did meet a girl named Max from California who had a step-brother named Billy who became their friend.
During the "final battle" in season 2 Mike was running around saying nonsense about Will being alive and possessed, El being alive and something about her sister? In the end they get Mike help, he's put on drugs since his parents insist that he doesn't need to be locked up.
Things get worse shortly after Dustin comes home from camp, unbeknownst to the party Mike wasn't taking his meds and has quickly declining. Suddenly Billy's possessed, Nancy's boss is possessed, there are Russians for some reason, and the new science teacher is and evil Russian?! It just gets even worse when the mall burns down, Hopper, Billy, and so many others unfortunately lost their lives that day, but Mike kept running around saying that it was the "Mind Flayer" and Hopper's alive but captured by the Russians.
So they do the only thing at makes sense at this point, they sent Mike to Pennhurst for treatment.
The party and his family visit and tell Mike about what's going on, about how highschool's going, about this new D&D group they found, that the Byers moved to California. Unfortunately it all gets filtered through his grief driven phyocosis. Mike also starts talking about another patient their Victor who went into a similar phycosis to Mike's after his family died, Mike starts talking about how Victor's dead son is alive and was the "demon" that killed Victors family and he's Venca and also One?
Mike makes less and less sense by the day, and when an earthquake happens, "Guys it's Venca." when a serial killers on the loose, ending the lives of Chrissy Cunningham, Fred Benson, Patrick McKinney, Jason Carver, and Eddie Munson, Mike blames it on "Vecna" aka "Henry" aka "One".
One by one the party stops visiting him, for their own sanity more than anything else, Max stopped when he wouldn't shut up about Billy and the "mind flayer", Lucas stopped when mike kept talking about his dead teammates like they were monsters, and Dustin stopped when mike saying Eddie died a hero, died fighting when it was really just tragic and traumatizing.
Without his friend's info on what's going on in Hawkins and their lives Mike's brain has to makeup even more stuff and makes even less sense somehow. Season 5 is the opposite of season one. None of it was really besides everyone's endings, since those were the last things they updated Mike on before going their separate ways, leaving him behind in Hawkins, their Master Storyteller.
I came up with this late at night and this post was not beta-read at all but I like Mike at to come up with something to cope and this was the result, I've been call this theory, Patient: M. Wheeler, for funsies.

















