Both the Duffers and Jamie himself confirmed that it was Vecna and ''Vecna and Will share a history'' I am not sure what kind of a history they share if Will just targeted by a mindless demogorgon and a mindless MF.
Also they outright show us that it was Henry through parallels, too. Will's possession scene in S2 is basically a parallel to how Chrissy gets Vecna'd. When Will is literally put in a trance in S2 and is being possessed, he closes his eyes and stands still like frozen. That's what happens to Vecna's victims in S4. The writers obviously modelled the scenes after each other and it was intentional.
Joyce and Eddie mimick each other too by both of them saying ''Will, honesy wake up!!'' and ''Chrissy, wake up!!'' and both Joyce and Eddie shaking Will and Chrissy by their arms and trying to end their trance.
I am sorry but I think it is kind of obvious that it was Henry? Not just the MF acting on his own. The demogorgon/s also dont act on their own either.
The way Henry's targets are experiencing Vecna's curse is similar to how Will was experiencing it in both S1 and S2. Because Will's both situations parallel Viktor Creel, Chrissy and Max's experiences.
It is really not the Mind Flayer. I am not sure why ppl keep denying this lol
yeah i think we might have a fundamentally different interpretation of the show dude. i have a theory about will’s history with henry here
those are 100% parallels, that’s a fact i cannot argue, but I think the intention of making those parallels was to show that henry and the mf have been working together since the beginning. the way will gets possessed is completely different from what henry does to his victims and will is shown to be in tune with the mf’s hivemind, as he becomes a part of its army, rather than experience what henry’s victims go through.
also, the creatures from the UD aren’t mindless. the way a hivemind works is that there’s a collective consciousness that unites all of the creatures, but that doesn’t mean they can’t do things on their own. the bats and vines willingly attacked, as if it were a hivemind response then henry would’ve been aware of the hawkins gang having been in the UD much sooner.
you can disagree with my interpretation of the supernatural stuff without being a bitch about it btw. if you weren’t aware. we can have conversations where you don’t sound like a pissy little asshole i promise it isn’t hard