Stranger Things introduced viewers to the Demogorgon in season 1, with the creature serving as one of the primary antagonists. Then in season 2, we learned that the Demogorgons are actually controlled by an enormous shadowy being called the Mind Flayer. The Mind Flayer is far more terrifying than the Demogorgons because it demonstrates an omniscient control of the Upside Down.
The Mind Flayer was definitely out for blood in season 3, when it possessed people in its search for Eleven (Millie Bobby Brown) and her friends. If you’ve ever wondered why this monster wants Eleven dead, then you’ve come to the right place.
Why does the Mind Flayer want Eleven?
All the way back in season 1, viewers learned that the Upside Down is a parallel dimension that exists in the shadows of our own. The Upside Down is a place that feeds off of death and decay.
The Upside Down, and by extension the Mind Flayer and the Demogorgons, seemingly thrives off of draining energy from living organisms. This was further demonstrated when Nancy found Barbara Holland’s body. It didn’t look like the Demogorgon had eaten Barb; instead, the creature just left her to rot.
The Upside Down’s affinity for killing other life forms was again shown in season 2 when the farmlands and forests around Hawkins Laboratory started to putrefy. Since the Mind Flayer’s connection to our world was growing ever stronger, the monster’s deathly invasion was quickly spreading.
In season 3, the monster took on a physical form using the decomposing bodies of Hawkins locals. We had to watch all those poor people chug chemicals and then dissolve into goo. You could say that heralding death is the Mind Flayer’s specialty.
Getting back to the question at hand, I think it’s pretty obvious why the Mind Flayer wants to kill Eleven. The monster wants revenge after Eleven stopped its spread into our world.
It was clearly displayed in season 2 that the Upside Down and its inhabitants harbor a grudge against Will for escaping in season 1. Once Eleven demonstrated her incredible powers to close the gate to the Upside Down, the Mind Flayer wanted revenge.
It specifically targeted Will in the show’s second season, so it makes sense that the monster’s focus shifted to Eleven in season 3. I think the creature would have taken pride in the fact that it eliminated someone so powerful. For the Mind Flayer, defeating Eleven and her friends is a revenge mission.