In this week's episode of Krypton, General Zod (Colin Salmon) finally finds a way to take control of Doomsday. As it turns out, Zod's key to achieving his goal lies in an alien plant called Black Mercy.
Krypton is littered with characters, locations, and concepts from the DC Comics universe, and it has already featured several classic villains, such as Lobo (Emmett J. Scanlan), General Zod (Colin Salmon), Brainiac (Blake Ritson), and a comic book-accurate Doomsday, one that has a new origin story. Another threat from the comics, Black Mercy, was teased for Krypton season 1 as far back as SDCC 2017, almost a year before the series premiered. Black Mercy eventually did appear, but not in any prominent way. The alien plant has been spotted in a glass case in Val-El's Fortress of Solitude. But now it has a much bigger role to play.
In Krypton season 2, episode 8, "Mercy", it's revealed that Lyta-Zod (Georgina Campbell) was cloned months ago, and the real Lyta was left paralyzed by a parasitic plant called Black Mercy. The alien lifeform placed Lyta in a dream-like state, making her believe that she was living a perfect life with Seg-El (Cameron Cuffe). Meanwhile, Zod found another use for Black Mercy that doesn't involve his mother. Zod now believes that if the toxins from Black Mercy's body are used on Doomsday, he can gain control of the powerful creature and send him to crush their enemies.
Much like Krypton's versions of Zod, Brainiac, Lobo, and Doomsday, the show's take on Black Mercy is a comic book-accurate interpretation. Debuting in Superman Annual #11 in 1985, Black Mercy feeds on a person's psychic energy by trapping them in a dream. While in this dream, the victim lives what they believe to be the perfect life. Like Lyta in Krypton, the victim has to discover the ruse before they can wake up. The plant infected some of DC's most iconic superheroes, such as Superman, Batman, Green Arrow, Aquaman, and Green Lantern. Black Mercy was also used in Supergirl.
While Black Mercy may not have much of a role in Krypton's remaining season 2 episodes, its unique traits may play an important part in the unfolding storyline. Zod wants Doomsday to become receptive to his commands, and one of Zod's scientists has discovered that Black Mercy's cells can place Doomsday in a "suggestive" state without subjecting him to Black Mercy's other psychoactive effects. Based on Doomsday's response to the toxins, it appears that their plan will work, which is bad news for Seg and the resistance. Zod believes that Doomsday is his best weapon, and considering that Doomsday is capable of killing Superman, he's probably correct. If Zod's plan is a success, the rebels' chances of defeating Zod will be significantly lowered.