Spoilers for Stranger Things season 5, episode 8.
The group enters the Upside Down for its final attack. Eleven, Kali and Max enter Henry's mind while the others climb toward the Abyss and the captive children. Military intervention disrupts the plan, and Kali is shot and apparently killed. Murray destroys the weapon suppressing Eleven's powers, allowing her to fight back. Henry pursues the children into the cave memories, where Will sees his connection with the Mind Flayer and urges him to resist; Henry refuses.
The Pain Tree holding Vecna and the children reveals itself as the dormant Mind Flayer. Eleven confronts Vecna inside it while her friends attack the creature from outside. Will restrains Vecna long enough for Eleven to impale him, and Joyce finishes him with an axe. The children are freed and the survivors escape. As explosives destroy the Upside Down, Eleven appears at the threshold, says goodbye to Mike and disappears with the collapsing world.
Eighteen months later, Hawkins has emerged from quarantine and the friends graduate. Dustin delivers his speech, the older friends discuss their new lives and promise to meet, and Hopper proposes to Joyce. During a final Dungeons & Dragons game, Mike offers a hopeful explanation that Kali created an illusion so Eleven could escape. He admits he cannot know whether it happened, and his friends choose to believe it. Holly and her friends take over the basement game as Mike closes the door.