Is Vecna The Mind Flayer In Stranger Things? Their Connection Explained
The way the various creatures are connected with one another in the "Stranger Things" universe can be a very complicated thing to understand, but what bonds Vecna to the Mind Flayer is comparatively simple. Once upon a time, Vecna was One, aka Henry Creel (Jamie Campbell Bower), a member of Dr. Brenner's group of wonderkids in Hawkins Laboratory. Eventually, Henry's malevolence results in Eleven (Millie Bobby Brown) banishing him to a primordial version of the Upside Down, which is where he manipulates one of the creatures already existing there into a spider-shaped being of pure elemental terror. It looks just like a drawing he made as a kid, to boot, and seems to be somewhat influenced by his long love of spiders. In short, he and the Mind Flayer are one and the same.
Whatever Vecna kills is absorbed into his consciousness, and he can harness its powers. He does sometimes have to take a more direct route, as he does with El after she defeats the Mind Flayer at the end of Season 2, when he implants a worm in her that sucks out her powers and transfers them to him. When Henry landed in the Upside Down, there wasn't anything there but gloom and rot — but that quickly changed. It was his doing that transformed it into a twisted version of Hawkins, and his actions that manipulated all of the creatures there into being his servants. Interestingly enough, though, prototypical versions of the Upside Down's creatures were already there when he arrived.
The Demodogs and other creatures from the Upside Down are connected to Henry, too
It wasn't just the Mind Flayer that Vecna could control. Demogorgons, demobats, and other creatures that live down in the Upside Down were already extant before Vecna arrived; they simply didn't have an organized purpose or act in a unified way until he interfered. It's important to note that above ground, when one is killed, all are killed, and when they attack, it's in a unified pattern. All of this is because they're being puppeteered by Vecna from his place in the Upside Down.
Vecna's ultimate dream is to remake humanity in his image, and since he's a psychopathic killer, that could be a bit horrifying for our gang of intrepid heroes. The fact that he maintains a parasite-like connection to anyone he tries to absorb into his army just adds to the danger. He's sent creature after creature to destroy El, even turning her friends against her. And despite them thwarting his plans on several occasions, he's still alive, and the Upside Down is invading Hawkins. The second half of the fifth season of "Stranger Things" should answer fans' biggest lingering questions about the Upside Down and reveal just how all-encompassing Vecna's powers ultimately are.