The illusion started right after Vol 1.
I see some people think it started after Ep 7, or in the epilogue but I personally think it happened after Volume 1.
Volume 1 Mike is entirely different than the Vol 2/3 Mike we see.
S5 Vol 1. Mike get’s Vecna’d theory
Drinking Coffee. We see him drink coffee twice, at the start of the season and in the hospital. Its also important to not that Nancy didn’t drink the cup Mike gave her nor did we see anyone else drink coffee. Coffee can do 2 things:
caffeine blocks adenosine, a brain chemical that promotes sleepiness. (Nightmares)
coffee can help headaches by narrowing swollen blood vessels and boosting pain relievers like aspirin. (Headaches)
Dozing off. Mike dozes (or dissociates) in the hospital scene. He didn’t hear Nancy talking to him and was only out of it after Nancy repeatedly shook him. (Like in a trance)
Clock chimes. A signature Vecna move. During the Mac-Z battle, Vecna doesn’t make any noise to alert anyone he arrives (so how did Mike see him?) When he arrives, a chime can be heard then Mike turns to look at him. (Mike also was the first)
I say Post Vol 1 and not Vol 2 because throughout Vol 2 we don’t see Mike experiencing any other symptoms anymore, Vol 2 Mike was also basically a cardboard cut-out, he was reduced to a background character.
Vol 2 is also where inconsistencies start:
Objects changing color. It starts in Camazotz, a world in Vecna’s mind. Examples are: the playground and the dial that turns the radio tower on.
Will acts weirdly. Vol 1 Will had hope for his ‘crush’, it then dissipates in Vol 2, that quickly? (Mike is not Will’s Tammy) In the tunnels, Will calls the children Vessels and Lucas and Mike look at him weirdly after, Will then immediately says that ‘it was what Henry told him’ (Will wouldn’t call the children vessels) Does Henry and Will’s mind start to fuse? Yes, it’s especially obvious during his coming out scene, he says these:
Melvald’s Diner, it was a convenience store Joyce worked at, the diner was in the 50’s during Henry’s time.
Getting lost in the woods, that’s literally his trauma why would that be any fun for him?
Calling Mike is Tammy and a crush, Mike is not a crush, he’s the love of Will’s heart. Tammy was someone Robin had a crush on, she was just her classmate nothing else. Mike and Will are best friends, since kindergarten. S1-2 Mike was very protective of Will too.
The checkers floor, it parallels to the scene with Henry and El in S4, where they play chess, and Henry had 12 pieces on the board, similar to the fact there were 12 people Will was coming out to (maybe that’s why there were people Will wasn’t close to)
Mike doesn’t show any symptoms but we see his hand switch in Vol 2, at the start of Ep 5, Kali’s illusion fails to keep up if she’s too far (Her hand is the one that is shown to support that)
Will and Mike drift apart in Vol 2/3, they never had scenes alone or any conversations after. (The radio tower scene was only added because Noah asked)
The epilogue is the ending Vecna shows Mike. (There are many evidences) He conforms his life, he becomes like his dad and drifts apart from his friends. Mike imagines the party living out their lives but not him. (“What about the storyteller?”) It’s weird they call Mike the storyteller when he’s their Paladin. (He’s still part of the story)
He imagines El far away in a journey, paralleling what the False Hydra can do.
Basically, it captures the town into a false reality. ✅ and for those who die, their loved ones will think that they are just far away, in their own journey, still alive. (El) ✅ El is dead. Kali’s injury was fatal that Hopper and El had left her, she wouldn’t have survived that long to create that illusion.
Its important to note that after they save Holly, she expels the Mindflayer. (Where does it go?) The Mindflayer in its gaseous (smoke) form is still alive, we see this in S2. After Joyce, Jonathan and Nancy expel the Mindflayer from Will using its weakness (heat), it travels to abandoned warehouse, where it then leads Billy and consumes him.
Mike is stuck in Vecna’s illusion, where its seemingly a happy ending but it’s not. He’s stuck in a world where he and his family conforms. This explains why it was so easy to kill Vecna and the Mindflayer (remember Eddie says you can’t kill Vecna because there’s still the Eye and Hand of Vecna’s? “It was just a thought.”)
Conformity is what’s killing the kids.