WARNING: The following contains spoilers for Stargirl Season 2, Episode 11, "Summer School: Chapter 11."
Eclipso has been a dangerous force to reckon with since Episode 1 of Stargirl Season 2. As a villain who preys on the fears, insecurities and traumas of all who encounter him, he has torn apart many people close to Courtney. He got Yolanda Montez to quit being Wildcat, he got Rick Tyler in jail, and he nearly tore Courtney's family apart when their darkest secrets came to light.
In Episode 10, The Shade told Courtney's family that the key to re-imprisoning Eclipso lied in putting the black diamond back together. What he didn't tell them was that doing so would summon Eclipso, and the intact diamond would give The Shade access to the Shadow Lands again, which would allow him to heal. The latter was really The Shade's goal -- one that nearly cost Courtney her life when Eclipso sent her to the same place he sent Cindy Burman earlier: the Shadow Lands.
When Courtney wakes up in Episode 11, she finds herself in a black and white version of Blue Valley where she encounters people who have already died, including the Zarick family. She also encounters a version of her mother who regretted having her. Furthermore, she sees how her desire to form a new JSA negatively impacted Yolanda and Rick.
While roaming this new black and white dimension, Courtney encounters Cindy, who attempts to kill her thinking she's another hallucination. When she sees Courtney bleeding from an injury, she realizes she's really there. Having spent some time in this strange dimension, Cindy describes this place as some sort of purgatory where a person's worst fears, traumas and regrets manifest. It's not until Courtney encounters the original Dr. Mid-Nite, Charles McNider, that she finds out where she really is: the Shadow Lands, aka the birthplace of Eclipso.
The Shadow Lands being Eclipso's place of origin makes sense. As Cindy herself experiences, the Shadow Lands repeatedly expose her to fears, regrets and traumatic life events, each time drawing her closer and closer to her breaking point. Cindy fears her father, so he threatens her in the Shadow Lands. She is also traumatized by his experiments on her, which she also relives here. The last nightmare that nearly causes her to break is the death of her mother, which is her greatest regret.
With the Shadow Lands being a manifestation of humanity's hatred and adverse life experiences, it can easily be described as a fate worse than death. All who fall within its depths eventually succumb to their hatred and are thoroughly destroyed as a result. The victims it claims provides Eclipso with the very fuel he needs to carry out his terror on the outside world. Now that Courtney, Charles and Cindy are aware of this detail, cutting Eclipso's access to the Shadow Lands may be the key to defeating him.
Stargirl Season 2 airs Tuesdays at 8 p.m. ET/PT on The CW.