In the season 4 episode "Dear Billy," Nancy and Robin discover that music just might be the only thing than can save people from Vecna's wrath. When Dustin and the gang pop Kate Bush's 1985 hit "Running Up That Hill (A Deal with God)" into Max's cassette player.
During the episode, Nancy and Robin learn that music is the only thing that can save people from Vecna's wrath. This bit of information proves useful as the gang is able to fend of the upside down demon and save Max using her favorite song Kate Bush's 1985 hit "Running Up That Hill (A Deal with God)."
Even though Max was free from Vecna, she died in Lucas' arms. She was dead for over a minute, until Eleven brought he back to life. However, there was one major ramification behind Eleven saving Max's life.
If Vecna has you in a trance, listening to your favorite song can help pull you out of it, as we saw when Vecna attacked Max only for her friends to pull her out his trance using the synth-tastic stylings of Kate Bush, specifically her 1985 hit “Running Up That Hill (A Deal with God).”
She breaks free, momentarily incapacitates Vecna, and runs with the determination to live toward her friends, dodging debris that Vecna throws in her path. Max hurls herself through the portal, awakes from the trance, and is held by Lucas (Caleb McLaughlin). "I thought we lost you," he cries. "I'm still here.
Vecna holds off Eleven long enough to brutally attack Max in his signature style—she levitates, her eyes go white and bleed, and he snaps her limbs. Eleven regains her strength and pushes Vecna off before he can complete the job, but the damage is already done.
Despite the best efforts of Eleven and Lucas, Vecna succeeds in wounding Max badly enough with the ritual that she dies. Eleven manages to revive her, but the minute that Max spent dead was enough to trigger Vecna's spell and open the gate.
After a certain period of time, Vecna will finally kill the victim by placing them into a comatose-like state, in which they will be unable to respond to outside stimuli.
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.
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.
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.
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.
While intending to get his revenge on Eleven and Brenner, Vecna also goes after victims who have dealt with traumatizing experiences in the past (reminiscent of his childhood and his time at the Hawkins lab).
Vecna was the one who originally kidnapped Will in season 1.
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 draws power from sad and angry memories and that is the main reason he targets traumatized teens. Those teens are a well of power just there to be absorbed. This is not just a theory, Vecna himself told Eleven about the power that angry and sad memories hold.
These visions build over time, and within a space of 24 hours Vecna's victims enter one final trance. There, Vecna taunts them, rejoicing in their heartache and sorrow, before killing them. Vecna's victims die in an agonizing way, lifted high into the air.
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.
Eleven has a memory during this episode and realizes that 001/Henry Creel (Jamie Campbell Bower) wants her to join him on his evil journey, and she banished him to the Upside Down. 001 then transformed into Vecna, the horrifying Stranger Things villain.
Realizing he had tremendous psychic power, he haunted his family with visions before ultimately killing most of them. His father was framed for the murders and locked away in a mental hospital as a disturbed serial killer. Henry then found himself in the care of Brenner, who decided he wanted more kids like the boy.
The trio gets upstairs and find Vecna strung up on his vines, unconscious while he deals with Eleven in the mind palace. They torch him with Molotov cocktails, and when he wakes up, Nancy shoots him with a sawed-off shotgun.
What does Vecna want with El? 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.
Vecna's obsession with time appears to be linked to his hatred of humanity. He views time as a human imposition on the natural world; an attempt to impose order on nature.
Following Eleven's resistance, Vecna sought after Eleven's 'power', which he identified as "a means to open [his] own doors" (gates).
After serving as bait for Vecna, she becomes his “final sacrifice,” getting her bones broken and losing her vision during a low point.