Joe Goldberg may be a cold-blooded serial killer with a penchant for locking the people in cages, but strangely, he also has a soft spot in his heart for kids in need of help. In Season 1, Joe helped his young neighbor Paco by killing his mom's abusive boyfriend, and in Season 2, Joe's parental instincts kicked in with his 15-year-old neighbor Ellie. Spoiler alert: This post contains spoilers from the You Season 2 finale. In the end, Joe isn't exactly able to help Ellie how he wanted, and the question of whether Ellie will expose Joe in You Season 3 looms large over the potential future of the series.
Aside from chasing his new love interest Love Quinn, protecting the precocious but vulnerable Ellie became Joe's main mission in Season 2. Joe first met Ellie when he moved into his new Los Angeles apartment, which was managed by Ellie's older sister Delilah. With Delilah always chasing a story as a journalist, Ellie was left to fend for herself a lot, and Joe soon noticed she was hanging around the skeevy comedian Henderson. After Delilah confided in Joe that Henderson had molested her when she was underage, he took it upon himself to be sure Ellie would not have to go through a similar experience.
Despite first trying to expose Henderson in non-lethal ways, of course, Joe wound up doing what he does best and killed Henderson after he caught the comedian attempting to drug Ellie. Although Joe was able to make the murder look like a suicide, Henderson's death only complicated his relationship with Ellie and Delilah.
Thanks to some clues from her police officer buddy Fincher, Delilah realized Joe may have killed Henderson, and she wound up discovering his cage... only for Joe to lock her up in it. Because of his genuine feelings for both Delilah and Ellie, Joe promised he would not hurt Delilah, and even made plans to free her in a matter of hours once he had time to flee the country. But Forty ruined those plans by slipping Joe acid, and Joe awoke from his trip to find out Delilah had been murdered.
That's when the big twist of the season was revealed: Love was actually the one to kill Delilah in order to protect Joe. Her plan was to pin Henderson's murder on Ellie, then use her family's influence to get her off. Joe was quick to shoot down the plan, and instead he secretly gave Ellie a backpack of cash and told her to go start her life elsewhere. It was not a touching farewell, though, as Joe revealed he killed Henderson and the Quinns killed Delilah, and Ellie angrily blamed Joe for ruining her life.
In the end, Ellie had restarted her life in Florida, with Joe periodically sending her money. But Ellie really seems like a big blindspot for Joe, and she has the potential to ruin his life in the future. She is the only person besides Love who knows Joe killed Henderson, and although she's relying on Joe for money now, she made it explicitly clear she hates him. On top of all that, she was also privy to Forty's movie script adaptation of Beck's story, which Candace later said basically spelled out Joe's previous murders. Ellie is a smart kid, so it is pretty safe to assume she will realize Joe was behind more than just Henderson's murder.
Given all this, Ellie is in a unique position to take down Joe at the end of Season 2. For now, though, fans will just have to wait to see if Netflix will pick up a third season of You, but given that cliffhanger ending and the show's popularity, it seems pretty likely.