One more thing about Vecna that seems to be out of discussion here.
When Max and Nancy visit the house in UD, it's still under construction and has the whole set is in the red lightning setting. But, when Vecna attacks in a trance he's attaching himself in the attic, so the house is intact, in an alternate setting of the UD - the blue/grey one we know from Season 1. Now, we also see the red, but formless UD, when 001 is banished by Eleven. Makes me wonder why is he rebuilding the house in that version of UD with the victims, also saying to "join him" and why there are two different versions of the house in UD itself.

One interesting thing is that, when Nancy gets trapped, she's in the pitch black "purgatory" for a second. Definitely Vecna used a different method of attacking her, as she had not been experiencing the clock visions.