Vecna Kept His Victims' Bodies To Possess Them Later, when Nancy ends up in Vecna's lair, she finds Fred in a similar situation. It's very likely Vecna has plans to use these bodies, which is why he didn't dispose of them like other Stranger Things villains have.
Vecna's powers allow him to form psychic connections with people in reality, especially teenagers dealing with trauma and mental health issues. Vecna develops these connections with young and vulnerable teens so that he can get out of the Upside Down and gain access to the real world by opening four gates or portals.
In the real world, he makes the victim levitate while in their trance, before snapping their bones and neck, and crushing their eyes. The murder site then becomes a small gate into the Upside Down, as part of a long term goal to apparently bleed both dimensions into one.
The aftermath of Chrissy, Fred, and Patrick's respective deaths shows their bodies remaining in the physical world to solidify that they hold a separate psychic existence in Vecna's Mindscape. Just as Max might be in Vecna going into Stranger Things season 5, Vecna takes the essence of his victims after killing them.
Why does Vecna mutilate his victims? Dr. Brenner (Matthew Modine) clarifies that Vecna "consumes" his victims, as he isn't interested in simply killing them - meaning Vecna takes everything about and from a person.
Max's past experience with trauma — namely, watching the Mind Flayer brutally kill her stepbrother Billy (Dacre Montgomery) in Season 3 — makes her a target for Vecna's manipulation.
And while his usual modus operandi is to embody his victims' negative self-talk (another very real psychological phenomenon), this time he is telling Nancy his plans and then releasing her so she can report back to everybody—Eleven included—that the end is nigh, with the goal of discouraging and disempowering them.
At his empire's height, Vecna was betrayed and destroyed by his most trusted lieutenant, a vampire called Kas the Bloody-Handed, using a magical sword that Vecna himself had crafted for him, now known as the Sword of Kas.
In the game, Vecna seeks power through artefacts, while in the series, he enhances his powers by consuming the essence of his victims, like the other gifted children in the lab, and absorbing their powers. When he took over the Mind Flayer, he gained control over the Demogorgons and other monsters.
(All of which have been cited by show creators the Duffer brothers as inspirations for the villain.) But he does have a surprising weakness: music.
Essentially, Vecna hates humanity, and wants to take over their world. He had hoped that Eleven would help him achieve this goal. But when he realised she wouldn't, Vecna instead used her.
Vecna lives in the Upside Down and preys on people's past traumas and guilt. The monster curses its victims, making them relive their trauma in progressively more gruesome ways until it violently kills them. (And we mean, like, really violently.)
Curiously, he also seems obsessed with time, projecting strange visions into his victims' minds—including of the grandfather clock from his home in the Creel House. Vecna's obsession with time appears to be linked to his hatred of humanity.
What is the significance of 4 for Vecna? The new season shows that the four chimes of the grandfather clock symbolize the four victims Vecna needs to claim in order to enter our dimension and take over humanity.
Vecna nabs Eleven and Max. Nancy, Robin and Steve, who were tasked to destroy Vecna's body when his soul is inside Mind Lair, also get trapped by his tentacles.
In the visions of her trauma induced by Vecna, Chrissy's mother appeared both mentally and emotionally abusive towards her daughter - and it's implied her comments about Chrissy's figure caused her daughter to develop her eating disorder.
In his twisted mind, Vecna believes that he his helping the world by wiping out humans, as a "predator, but for good." When Vecna asks for El to join him, it's because he also sees her as a predator, "better" than humans. He offers her his path as a sort of freedom, as they reshaped the world in their image.
Vecna hated humanity, believing human beings had imposed an artificial order upon the natural world.
Vecna's use of his victims' guilty conscious to terrorize his prey is an obvious tool in his arsenal. What is more subtle and powerful is that he uses shame to isolate and control. All of his victims, starting with Henry's father, believe that if people know the truth about them, they will face rejection.
Vecna's Hand
This is a reference to the D&D character Vecna, for whom this Vecna is named; the D&D Vecna has a monstrous hand infused with dark magic. The design of Vecna's hand is also a nod to Freddy Krueger, the Nightmare on Elm Street villain who had a huge influence on this season in general.
Together, their powers combined are the exact powers of 001/Henry. Fans are now theorising that the powers of both 011 and 008, who have the combined power of 001, is what is needed to finally match and defeat Vecna. To put it simply, 011 + 008 + [with the combined power of] 001 = 020, a.k.a. Erica's critical hit.
Combined with the fact that Dr. Brenner (Matthew Modine) states in the Stranger Things episode "Papa" that Vecna "consumes" everything about his victims, Vecna targets traumatized victims because it builds for him a well of sad and angry memories to draw from. With each victim, he can become gradually more powerful.
Next up, the viewers go on to theorise that One/Vecna is actually Eleven's dad. Yep, told you it was wild. The theory claims that Brenner wanted to create a child with stronger powers, so he waited until One was old enough to become a father.
Eleven defeats Vecna (Jamie Campbell Bower) in a psychic battle, Steve and Nancy light his body on fire, and Nancy shoots him several times with a sawed-off shotgun. But it's not enough. Vecna's body goes flying out the window of the Upside Down Creel house and he lands with a thud.
1. Is Nancy OK? Yes! Nancy (Natalia Dyer) is fine — at least, as fine as she can be after being traumatized by Vecna (Jamie Campbell Bower) and almost strangled to death by his squelchy, squelchy tentacles. Instead of escaping Vecna's Mind Lair by hearing her favorite song, Nancy is actually released by Vecna himself.