Stranger Things - Season 4eps9 -

Eleven uses a makeshift isolation tank in Nevada to psychically enter Max’s mind and fight Vecna from within. Major Deaths & Sacrifices

Despite the team's efforts, Vecna technically wins the battle. Because Max died (even briefly), the fourth gate opened, causing a massive "earthquake" that tore through Hawkins.

Vecna reveals he discovered the "shadow" particles in the Upside Down and shaped them into the Mind Flayer to act as his tool. Stranger Things - Season 4Eps9

The episode famously featured Metallica's "Master of Puppets" and a mashup of "Running Up That Hill" with the show's theme.

In a heroic turn, Eddie refuses to run and stays behind to lure the bats away from Dustin. He dies in Dustin’s arms, finally proving to himself he isn't a coward. Eleven uses a makeshift isolation tank in Nevada

The Hawkins group executes a high-stakes mission to kill Vecna by attacking him on three fronts simultaneously:

Steve, Nancy, and Robin infiltrate the Upside Down Creel House to destroy Vecna’s physical body with Molotov cocktails and shotguns. Vecna reveals he discovered the "shadow" particles in

"Papa" dies in the desert after being shot down by military forces while trying to save Eleven (at the end of Episode 8/start of 9). 🔓 The Ending Explained