You ready? Eleven is the monster. She, like the Demogorgon in Dungeons & Dragons, has two opposing sides. In the game, the Demogorgon literally has two heads — one destructive and one deceptive. If we follow that same model, Eleven would be the deceptive side and the monster the destructive one. The theory, solidified by a convincing video via UpRoxx, points out that we first meet the monster when Eleven is isolated in that creepy pitch-black room. The monster could easily be a manifestation of Eleven's own evil side. This theory accurately plays into the whole theme of dichotomy on the show. The real world is sunny, colorful, and bright. The upside-down world is bleak, ashy, and decrepit. Total opposites. When Eleven has her final one-on-one battle with the monster to save her new friends, she lifts her hand to harness her powers. In return, the monster does the same, as if mirroring her body's motions. Is this because they are mirror images of each other? Is this why Eleven turns to ash herself? Did she give herself up to the monster, a.k.a. her dark side?