Vecna successfully stole
That's because Vecna wanted to take and understand Eleven's powers. In particular, Vecna wanted to know how Eleven was able to open gates to the Upside Down. So, rather than killing Eleven, the Spider Monster lodged itself inside Eleven's leg to sap her powers and learn her secrets.
Even months after the group defeated the Shadow Monster, Eleven was still without her special abilities. Somehow, the Mind Flayer was able to absorb her powers after it bit her.
Vecna seemingly acquired Eleven's ability to influence minds from across dimensions after a piece of the Mind Flayer's proxy body bit Eleven in July 1985, a being that the possessed Billy said was “made for” her.
Stranger Things' Vecna Identity Twist Explained
Stranger Things season 4, volume 1 revealed Vecna's origin story. He was originally Henry Creel, son of Victor Creel. Eleven and her siblings gained their powers as a result of Dr. Brenner's experiments, but Henry Creel was born with them.
"I walked up to her [as Vecna] and she burst into tears. She wouldn't look at me and she was visibly just disgusted by the whole thing... After she cried and I made it obvious that she knew it was me, one of the things she said was that, 'I knew it was you when I could smell cigarettes,' because I'm a smoker."
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.
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).
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.
After seeing their second fight, it was clear that Vecna was stronger than Eleven one-on-one, so in Season 5, Eleven will have to find a way to upgrade her powers in order to vanquish her foe once and for all. Stranger Things Seasons 1-4 are streaming now on Netflix.
During one of her many encounters with it, Eleven was bitten by the shadowy demon, which leaves a parasitic piece of it wiggling around Hawkins, Indiana. While Hawkins Police Chief Jim Hopper (David Harbour) manages to squish the evil critter, it first sucked Eleven's powers like a leech.
I saw a means to realize my potential, to transcend my human form, to become the predator I was always born to be. Vecna reached out to the Mind Flayer, seemingly using his powers to reshape it into the spider-legged monster he had doodled as a child.
The reason that Eleven couldn't find Max is actually pretty simple -- Max had already died. That means her soul had already been absorbed into Vecna's consciousness. So, while Eleven restarted Max's heart and brought her body back to life, she was trapped inside of Vecna's hive mind.
Henry spends years trapped in the Upside Down, which changes him into the monster that is now terrorizing Hawkins in the present: Vecna.
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.
Vecna successfully stole Eleven's powers when controlling the Mind Flayer in Stranger Things' season 3 ending, which finally allowed him to emerge stronger than Eleven and enact his plan to take over Hawkins with the Upside Down.
His main weakness is not any particular set of traits, but a constraint imposed by his location: the Chaotic Quest entrance is a portal rather than a staircase, and Vecna is covetous. Vecna will therefore readily warp to you, but will not teleport away to heal.
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.
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.
As Vecna, he uses these mental abilities as a way to psychologically weaken and lure in his victims – much in a way that Pennywise, Freddie Kruger, and Pinhead do. (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.
"Vecna seems to be actually intrigued by Nancy being able to figure him out, to be able to get this close to the truth... I think this is more Vecna's narcissistic traits that pull him to Nancy, why he wants to give her this information."
When One massacres the rest of the children in Hawkins Lab, Eleven banishes him to the Upside Down in the same way she banishes the Demogorgon from season one. One is sent hurtling through the Mind Flayer's lightning and is horribly disfigured, transforming into Vecna.
He's the infamous Number One, but had his powers blocked and worked as an aide in the Hawkins National Lab. He befriended Eleven at the lab and not knowing Vecna was evil, Eleven restored his powers resulting in the massacre and his expulsion to the Upside Down.
In the series, Eleven is shown moments from her past at Hawkins Laboratory, right up until she manages to banish Vecna into the Upside Down.
Sharing more about Eleven's real father Andrew Rich could be a great way to wrap up the story.