Vecna's curse refers to Vecna's predominant method of murder and torture. Using his supernatural psychokinetic abilities, Vecna can probe and influence the minds of others. Motivated by a cruel and misanthropic philosophy, Vecna targets particularly traumatized, mentally ill or insecure individuals.
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.)
Vecna puts a curse on his victims by finding people who are dealing with tragedies and negative feelings like low self-esteem. When he has begun his process, his victims feel sick, their noses bleed, they have headaches, and they see things that aren't really there, such as a grandfather clock.
After learning how Victor Creel was able to evade death back in 1959, Robin and Nancy deduce that playing the victim's favorite song can help them escape the trance that Vecna places them in, with music and happy memories being the only way to keep Vecna's fatal curse at bay.
While the source of Vecna's powers is never explained, there are some Stranger Things hints leading to the theory that Hawkins had a big part in awakening them. Vecna is revealed in season 4 to be the base cause behind all of Hawkins' unfortunate happenings for the past three years.
The Upside Down is first expected to be exposed to the real world in 1979, during Eleven's fight with One/Henry Creel in the Rainbow Room of the Hwakins Laboratory when Eleven unintentionally opened the gate while overpowering One, sending him to the dark world, where One became Vecna.
In the D&D realm, a defining feature of Vecna is that he's missing his left hand and left eye. This is because his trusted accomplice, Kas the Bloody-Handed, betrayed him and used the sword Vecna created himself to chop off his left hand and remove his left eye. This ultimately destroyed Vecna.
(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.
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.
School newspaper reporter Fred Benson (Logan Riley Bruner) fled from a deadly car accident that continues to haunt him. Patrick was targeted due to his father's abuse of him. Finally, Vecna targets Max for her trauma from witnessing Billy's death and uses Barb's (Shannon Purser) death as a way to use Nancy.
Ultimately, it is revealed in Stranger Things season 4's finale that the reason why Vecna was killing Hawkins teenagers was to create a massive gate that merges the Right Side Up with the Upside Down - and he specifically needed four bodies to do so.
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.
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.
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.
Music evokes strong memories that are both good and bad, so it makes sense that it could open a doorway out of the oppressive alienation of trauma, despair, and guilt that Max found herself in.
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.
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).
"The reason why Vecna only has a single eye and hand is due to a betrayal by Kas", who used the sword against his former master. "In the third edition of Dungeons & Dragons, the Sword of Kas is a +6 unholy keen vorpal longsword that grants a +10 modifier to the Strength score of its wielder".
From the beginning, Vecna was a long-vanquished lich—a wizard who used dark forbidden magics to keep themselves effectively immortal but in a perpetual state of undead decay—and while DMs were free to use their imagination and flesh him out into a proper villain, his only official existence in the old D&D books was as ...
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.
Vecna hated humanity, believing human beings had imposed an artificial order upon the natural world.
Vecna seeks four victims in total. His first three victims — Chrissy Cunningham, Patrick McKinney, and Fred Benson — are all peers of The Party, people they know from school, which makes Vecna's terror all the more real.
Vecna isn't as terrifying in the bathroom. Actor Jamie Campbell Bower, who played the complicated villain in “Stranger Things 4,” revealed that his terrifying Freddy Krueger-esque full-body prosthetics included a “flap” for him to use the restroom without getting out of costume.
While in this trance, Vecna will stalk his victim, chasing them through his mind, the victim's mind, and whatever strange psychic realms lie in-between. If Vecna can overwhelm their victim with fear, and keep them from resisting, their fate is almost certainly sealed.
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. Their every joint is twisted out of shape by Vecna's telekinesis, making for a horrific spectacle.