So this scene is like high-fiving a mirror.
Obviously, adorable little Eleven didn't control the monster, but the show has hinted that the two were linked. Eleven is the first person to encounter the monster, after she finds herself transported to a dark dimension during an Altered States-on-steroids experiment. But what if that place was her subconscious, and the monster a manifestation of her psyche? You'd feel pretty monstrous too if some dicks experimented on your brain all your life.
Later on, the show's nerdy protagonists name the monster after the Demogorgon from Dungeons & Dragons ... which you'll note has two heads, and even two personalities.
And usually a thick coating of Cheeto dust.
Also, in the very first episode, the kids reference X-Men 134, which comic fans all know features the first appearance of Jean Grey as Dark Phoenix. You know, "The Dark Pheonix Saga," that story in which a good, psychokinetic female character turns evil against her will and goes on a crazy kill-spree?
If that kid held onto that comic, he's now a $75-aire.
In fact, as Vox points out, the show is full of references to the "Dark Phoenix" story, like when Eleven throws the villain into a wall, or when she turns it (and herself) into ashes:
Key difference: Stranger Things characters don't talk in five-minute soliloquies.
If that isn't enough for you, in one scene, she flat out states she's the monster. Which the kids quickly dismiss, because kids are dumb.
"I'm literally the monster, you idiot."
"Aren't we all literally the monster, in a way?"
What if she's been trying to confess that the monster is a manifestation of her powers she can't control? If this is the direction season two is headed, Eggo might want to think twice about doing any product placements in which they're the preferred frozen waffle of Lovecraftian murder-beasts everywhere.
And speaking of those filthy muties ...