The spider-like creature stands around 50 ft tall and has the capability to possess victims via particles, taking control of their brains from the Upside Down.
It first appeared in the second season, and its first victim was Will Byers, who was under its shadowy control. While Byers was eventually saved by his friends, it was Max Mayfield’s half-brother, Billy Hargrove, who was killed by the monster in season 3. The Mind Flayer is one of the most powerful creatures, but in season 4, it is revealed that Vecna is the one who actually controls it.
