The all-new episode of "Supergirl" season 3 next week will introduce a character that might be the key in saving the world from the clutches of Reign (Odette Annable), the present season's big bad. However, in episode 13, titled "Both Sides Now," the only hope for Kara Danvers (Melissa Benoist) to stop Reign will unleash its destructive powers inside the city, making her just as much of a threat as the villain that they are trying to defeat.

"Supergirl" season 3 episode 13 will introduce the second World Killer named Purity, to be portrayed by actress Krys Marshall. According to the promo teasers provided by the CW, the new World Killer, who happens to be the sister of Reign, appears to be harmless at first. However, when Kara and DEO attempt to subdue Purity, the latter will be forced to show everyone just how powerful and dangerous a World Killer can be. 

A promo clip for "Supergirl" season 3 episode 13 shows the first encounter of Kara with Purity, and it seems like Supergirl's power is no match for Reign's sister. Purity is shown to be raging mad at the people who are trying to capture her, and her attack against Kara immediately weakened the red-caped heroine.

The spoilers suggest that Purity is half-way between joining her sister Reign to destroy Earth and cooperating with Supergirl on how to stop the menacing World Killer. A promo clip seems to confirm that Purity will become allies with Reign as the duo destroys a portion of the National City. However, with Kara showing her good intention to save the world while interrogating Purity, it is possible that the latter will decide to offer her help.

The DEO's method of questioning Purity might be the reason for the second World Killer to wreak havoc, ultimately escaping from its premises. Nevertheless, with the kind of power that Reign has, there might be no other way to stop her aside from using the power of another World Killer. Meanwhile, "Supergirl" season 3 episode 13 will also see J'onn (David Harewood), Winn (Jeremy Jordan), and Mon-El (Christopher Wood) trying their best to repair the Legion ship.

"Supergirl" season 3 episode 13 will air on Monday, Feb. 5, 8 p.m. EST on the CW.