#will getting vecna'd

But what if it isn't stuck? What if it looks like that because of Will?

Vecna said that when he arrived at the Upside Down, it was all shadow and darkness, by that we can suppose it was empty. So how Will could hide in Castle Byers if it didn't exist?

We could say Vecna molded that dimension to look like Hawkins because he lived there, he knows that place. But Henry was in Hawkins lab since 1959 and after that, the Upside Down. So is entirely impossible for him to know about Castle Byers.

And since Will left the Upside Down, he had a connection to it. But just him, not Nancy, Joyce, Hopper, Steve, or Robin. That's suspicious. Even more suspicious that that connection stayed after the Mind Flayer left Will's body.

It means that Vecna needs something from him. And what does he need? Will's mind.

We know Will likes to draw, that is a fact since s1. And that trait of his has been important for the plot of s2. Also, it stated that he has a creative mind.

And is exactly that what Vecna needs.

When Will entered the Upside Down, he shaped it to what he wanted more at that moment, home. The place took the appearance of Hawkins from his time, something that Vecna hadn't been able to accomplish no matter what he did.