Stranger Things Season 5 is gearing up to it's finale. If you're an avid Stranger Things fan, you know that the Upside Down and its mysterious creatures (especially Vecna) have been the number 1 villain for Team Hawkins.
But Volume 2 of Stranger Things Season 5 sort of destroys this theory. When Nancy shoots the exotic matter, and things begin to melt, Dustin rushes to the rooftop to rescue them. Turns out, as per Dr. Brenner's notes, the Upside Down isn't a different dimension; it's a wormhole that leads to a different realm, which they call the abyss. It is here that Henry Creel became the dangerous Vecna, and it is home to the other nasty creatures that have caused chaos to date.
But is Vecna really the only villain in Stranger Things, or is there something else behind it all? Sure, Vecna has been responsible for the nastiest things in the series, right from Will Byer's disappearance, to uncountable deaths, to Max's comatose condition, and most recently, the kidnapping of the twelve children, and even more.
Turns out the real monster isn't Vecna but the scientists.
Here's more about it.
Stranger Things Season 5: Volume 2 reveals that the bad guy isn't Vecna but the scientists

Vecna might be one of the most disliked guys in The Stranger Things universe, but he's not the real bad guy. Volume 2 of Stranger Things Season 5 clarifies this. After El and Jim Hooper rescue Kali from the lab led by Dr. Kay, Kali reveals to El the cruel experiments that the scientists have done on her. She reveals that Dr. Kay drugged her and extracted blood from her. One day, when she attempted to escape the lab, she stepped into a room where she saw a pregnant woman being infused with her blood. As she ran to escape, she saw more pregnant women in the same condition until she was caught by the guards.
Turns out Dr. Kay has restarted Dr. Brenner's cruel experiment to infuse the pregnant women with their (children with powers) blood to create more such children to fight their enemies. To top it all, it's a government-funded programme and the military aids them (although they have little to no information about the details of the nasty experiment). Just like how Henry's blood was used to create El and others, Kali's blood was being drawn and infused into the pregnant women in hopes of recreating children with special powers.
Kali also urges El to rethink that no matter where they escape, Dr. Kay or even her successor will continue with such experiments as long as they are alive. She tells El that the only way to end it all was to kill Vecna in the Upside Down and remain inside it to avoid them being misused again. However, whether El gives in to this thought or not remains a mystery.
Who is Dr. Kay in Stranger Things Season 5?

Dr. Kay, played by Linda Hamilton, is an antagonist in Stranger Things Season 5. She's a scientist who is eager to restart Dr. Brenner's super soldier programme, which uses the blood of children with special powers like Eleven or Kali to create more children like them. She's ruthless and determined.
In Volume 2, when she finds that Kali is missing, she grows furious, and she orders the military to start searching for her. She even threatens Lt. Akers, who simply questions why she is obsessed with finding the girl (Kali or El). She says,
"Everything that's happened here is because of that girl. And if you had just done your job and found her , then I wouldn't have to repeat myself and we'd have those monsters in Moscow where they'd killing Soviets instead of Americans."
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