Steve Harrington and the younger kids lure the Demodogs away from the lab by setting fire to the "hub" in the Upside Down tunnels.

Eleven and Jim Hopper descend into the lab's depths. Channeling her trauma and anger, Eleven uses her telekinetic powers to force the gate shut, severing the Mind Flayer's connection to Earth.

One month later, the lab is shut down. The season ends with the bittersweet Snow Ball dance, though a final shot reveals the Mind Flayer looming over the school in the Upside Down. Season 4, Chapter Nine: "The Piggyback" The Piggyback | Stranger Things Wiki | Fandom

In the Stranger Things universe, there are two distinct season finales titled "Chapter Nine," both of which serve as major turning points for the series.

To safely close the gate, Joyce Byers , Jonathan , and Nancy Wheeler "sweat out" the monster from Will using extreme heat at Hopper's cabin.