SPOILER WARNING: This article contains major spoilers for "Schott Through the Heart," the latest episode of Supergirl.
Supergirl has finally revealed the Legion of Super-Heroes' true mission, which was teased in the last episode. At the end of "Schott Through the Heart," the latest episode, Mon-El told Kara that the Legion had traveled back in time to stop Pestilence -- the as-yet undiscovered third Worldkiller -- from becoming the Blight and destroying a planet.
As Winn and his mother performed at karaoke night, Mon-El pulled Kara aside to fill her in on this. "I actually wasn't going to talk about Imra. I mean, not about my feelings, but I felt like you needed to know what she did and why she did it because it directly affects you," he explained. "The Legion didn't land here by accident."
"Wait, I thought you hit a disruption?" she asked.
"Yeah, we did, but Brainy and Imra hit it intentionally and they hid the real mission from me because they didn't trust that I'd want to come back to this time," he revealed. When she asked about the mission, he continued, "Well, the third Worldkiller -- the one you haven't found yet, Pestilence -- in a thousand years, she evolves into Blight. So if we can find her now, in this time, then we can save everyone today and in the future. And look, we have a common enemy now, so we can work together."
Here, Mon-El is referring to the destruction of the planet Winath, the home world of his fellow Legionnaire Ayla. In the episode “Legion of Super-Heroes,” which aired in January, the Legion told J'onn and Alex about a threat from the future called the Blight. According to Imra, the Blight "consume[s] everything in their path," including the entire planet of Winath.
To combat this threat, the Legion came up with a way to stop the Blight and "hid the information in the safest place we could: our DNA, where it can’t be lost, it can’t be stolen. It’s written in our genes.” As such, the Legion may literally be the key to stopping the Worldkillers. If they can stop one Worldkiller with the information they have stored in their genes, they may be able to stop the others as well. However, it is unclear if that solution would also mean the death of Samantha Arias and Julia Freeman, the Worldkillers' alter egos.
Airing Mondays at 8 p.m. on The CW, Supergirl stars Melissa Benoist as the Girl of Steel, David Harewood as Martian Manhunter, Mehcad Brooks as Jimmy Olsen, Chyler Leigh as Alex Danvers and Jeremy Jordan as Winn Schott, with appearances by Calista Flockhart as Cat Grant and Tyler Hoechlin as Superman.