Through his "curse" power, Vecna began tormenting and killing various Hawkins residents; with every murder, a new gate would open at the site of the victim's death. Vecna took the lives of Chrissy Cunningham, Fred Benson, Patrick McKinney and Max Mayfield.
As Vecna continued to go after young victims in order to open more portals, he set his sights on Max Mayfield, since she was investigating the deaths of Chrissy and another student named Fred Benson with help from her friends (including Dustin, Steve, and her boyfriend Lucas).
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.
Based on the flashback in “The Hellfire Club”, he killed an estimated 21 people: 13 lab subjects, two orderlies, two guards, Ten, Alec, Dr. Ellis, and Six. A flashback during “The Massacre at Hawkins Lab” later reveals that Vecna killed even more people in Hawkins Lab than we thought.
His first victim was Chrissy Cunningham. Vecna targeted Chrissy by using her depression and eating disorder against her in his visions. Chrissy was killed in Eddie Munson's trailer, and the first gate was opened on the ceiling.
While caught in Vecna's grip, a tear in the dark dimension reveals her friends on the other side, desperately trying to save her from Vecna's curse. Of course, it's "Running Up That Hill," blasted into Max's headphones that breaks Vecna's hold on her.
Hawkins has suffered a lot of trauma over the years - not all of which is connected to Hawkins Lab and the Upside Down - and Vecna's curse takes advantage of that. Vecna appears to carefully choose people who feel a strong sense of guilt or shame, particularly if those emotions are repressed.
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.
(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.
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.
Vecna's first season 4 victim is Chrissy Cunningham (Grace Van Dien), who is targeted based on the trauma she carries due to her body-shaming mother.
Once he takes control of the mind, he traumatizes them by showing the visions of their dark past. He takes them to unknown places and gives them a glimpse of himself. The pain of his victims doesn't end here. Every single one of his victims experiences nose bleeding and severe headaches as well.
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.
Though Fred appeared to be bright and level-headed, he harbored extreme guilt for his role in the fatal 1985 car accident, and believed many people look at him as a "murderer." This guilt and mental unrest made him a target of Vecna.
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.
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.
The theory is that Karen Wheeler might be Vecna's sister, Alice Creel. As we know, Vecna is actually a man of many names, including 001, Peter Ballard and Henry Creel. We saw Henry and Alice together as children briefly in a flashback and it is believed that Henry killed his sister along with his mother.
The theory predicts that Vecna wants to regain his human form, and he will use Will to do so in Season 5. Knowing that Vecna singled out Will in Season 1, it's a reasonable theory, but it might go too far. After all, Vecna already has a human form, and he has vowed to eliminate humanity.
He didn't name himself Vecna, the kids did. They named him after a DnD character who's a wizard, since Vecna's curse sounds like something a dark wizard would do.
We know Eleven was born in 1971, which means her mom got pregnant with her during the tests, sometime in 1970. A 1959 flashback in the mid-season 4 finale reveals a 12-year-old One (Jamie Campbell Bower). That puts One, a.k.a. Vecna, as 24 when Eleven was born.
"Vecna really is a creature that has mutated in the last however many couple of decades during his time in the Upside Down," prosthetics designer Barrie Gower said. "This is where he has become more overtaken by the Upside Down world and become pretty much possessed and mutated."
This ultimately destroyed Vecna. Though they're clouded with cataracts, Vecna in Stranger Things has both of his eyes.
Physically, yes. Lucas tells his friends that Max is in a coma, and we see her wearing casts on her arms and legs. The Duffer brothers have also confirmed that at the end of Season 4, Max is alive yet "brain dead, blind, and all of her bones are broken." The big mystery is where the redhead is mentally.
In the final moments, Max is in a coma. With that said, if Max were to make a full recovery, would she be blind? Well, based on the injuries she sustained, it's likely Max will be blind going forward.