One of the most controversial and confusing scenes in season 3 of Stranger Things came when Billy Hargrove (Dacre Montgomery) got possessed by the Mind Flayer. In the episode, he's a total jerk who bullies the young Hawkins gang before being ripped apart by the monster. Billy's character seemed to be headed for a total arc of darkness, but his last moments on the show were actually heartwarming.
When he lays his hands on Eleven, she resists at first, but eventually gives in and starts fighting back against the possessed Billy. During this battle, she also uses her powers to give Billy memories of his happy childhood and even more so, his late mother. These memories, paired with the fight against the possessed Billy, helped to make him realize what he had done and broke free of the Mind Flayer's control.
Sadly, this didn't help enough to save Billy from being brutally stabbed by the monster and dying. However, it did stop the Mind Flayer from being able to kill Eleven in the process, which was what he had been trying to do all along.
While many fans have a lot of mixed feelings about Billy's death, there is no doubt that he made a huge sacrifice that saved both his step-sister Max and the entire town of Hawkins. Despite this, some viewers are still wondering if the Duffer Brothers will ever bring him back or not.