They Just Reintroduced Superman’s Deadliest Kryptonite

Kryptonite has always been the deadliest weakness of all Kryptonians. It comes in all varieties of colors and effects, from the classic green that acts as poison, to the gold version that permanently strips a Kryptonian of their powers. One of the most dangerous types of Kryptonite, however, is Black Kryptonite. This onyx-colored rock doesn’t directly harm Superman or any other survivors of his home planet, but instead it brings out the darkness that lives inside of them. It turns them into weapons that will tear apart everything they care about, and there are very few things harder to stop than a murderous Kryptonian. As of Supergirl (2025) #3, this Kryptonite is back and deadlier than ever, and the Woman of Steel had her entire being inverted, becoming the vile monster known as Satan Girl.

What Is Black Kryptonite?

Like most other forms of the deadly element, Black Kryptonite emerged with the explosion of Krypton. It actually originally debuted in the Smallville episode “Crusade,” and made its comic book debut in Supergirl (2005) #2. Those two appearances showed it as separating the affected person into two halves; one good, and one evil. However, all of its subsequent uses have instead depicted it as altering the mind of the person it affects, inverting their morality and turning them into murderous monsters. It made its first post-New 52 appearance in The Batman Who Laughs #1, where the Dark Multiverse version of Batman used it to have Superman and Jon Kent kill their family before it killed them. However, that was a different universe, and for a long time Black Kryptonite was absent from the main DC Universe. Now it’s back, and worse than ever.

Rise of Satan Girl and Krypto the Satan Dog

Supergirl is dealing with an imposter. Her hometown of Midvale has been convinced that Lesla-Lar, a Kryptonian from the Bottle City of Kandor, is the real Supergirl, and Kara is the imposter. She’s gone as far as to brainwash the Danvers into thinking she was their daughter instead of Kara, and the only person still on Kara’s side is Lena Luthor. Still, even if the entire town is calling her Phonygirl, that’s not going to stop Kara from being a hero. She continued to fly about Midvale and solve problems, getting everyone to love her, even if they think she’s trying to cut in on Supergirl’s fame. Lesla-Lar, meanwhile, is completely taken aback that the town turns on her so quickly. She is obsessed with Supergirl and desperately jealous of the attention she receives, but fails to understand that people treat her well because she is a hero who isn’t seeking reward. Wanting the town to hate Supergirl as much as Lesla does, she exposes the superheroine to Black Kryptonite. Supergirl and Krypto are completely transformed into moralless villains, with Kara redubbing herself Satan Girl.

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Satan Girl and her super-evil dog fly about Midvale causing all kinds of mayhem. She pantses an entire street, vandalizes Midvale High, and even ruins a kid’s birthday party. Krypto, for his part, melts someone’s car with super-heated urine, which is the worst way to lose a car. Lesla-lar expects the town to love her after she reveals Kara’s darkness, but they reject her for doing everything for attention. Lesla is taken aback, and completely flabbergasted when Satan Girl starts terrorizing the Danvers. Seeing people who have only treated her with kindness being hurt, Lesla tries to stop the rogue girl, but Kara is completely out of control. Worse, her body and mind start to deteriorate from the Black Kryptonite exposure, turning their problem from bad to disintegrating Supergirl bad. Thankfully, that’s around when Supergirl’s new bestie Lena Luthor and Streaky the Super-Cat show up. Lena uses the recently miniaturized Titano’s Kryptonite eye-beams to disinfect Satan Girl, returning her and Krypto to normal.

The one and only Supergirl once more, Kara looks to Lesla-Lar. The jealous villain is ready to accept whatever punishment Supergirl dishes out, but the Maiden of Might instead hugs her, and tells her that things have to change. She understands the loneliness that drove Lesla to do all of this, and wants to help. Unfortunately for that heartwarming moment, a portal opens up, revealing Lesla-Lar’s parents, members of the Kandorian Science Council. They declare that Lesla has broken Kandorian law by coming to Earth and causing havoc, and Supergirl is to blame for her influence over her. They announce that both girls are to be transported back to Kandor for immediate judgement. 

Stuff’s not looking great for Supergirl, but at the very least she survived this encounter with Black Kryptonite. Still, Kryptonite of all types is way more plentiful thanks to the events of Superman Unlimited, so it’s highly likely that we’ll be seeing more of the deadly rock in the coming years. It’s definitely the last type of Kryptonite I’d want to run into, and the entire Super Family is going to have to keep their heads on swivels to avoid it. 

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