The DEO recruits Lena in their fight against the World Killers, but the alliance is an uneasy one.
Tropes:
- Abnormal Ammo: Winn makes Alex a new outfit with a gun that fires bullets which explode with enough force to knock down Reign.
- All for Nothing: Lena is heartbroken at the beginning, since all of her research on Reign was basically rendered useless and she strained her relationship with Supergirl in the process. Although it's not a total loss given Lena discovered the World Killer dimension.
- Another Dimension: The Dark World Sam was sent to last episode isn't some Mental World confined to her own head, but another dimension all the World Killers are connected to.
- Antagonist Title: The title refers to the three World Killers. Doubles as Team Title.
- Armor-Piercing Question: When Supergirl is reading Lena the riot act over keeping secrets, Lena counters by asking her for her real name, pointing out that she keeps secrets too.
- Artistic License – Space: Solar eclipses do not cause substantial temperature drops on Earth as suggested in the episode. A lack of sunlight would eventually freeze the planet, but the episode makes it sound like it would happen instantly. And, since Kara doesn't lose her powers at night, the blocking of the sun's rays by an eclipse should not immediately impact her powers as it does. The latter is implicitly justified by magic, but the former is made to sound like a normal effect of an eclipse.
- A Wizard Did It: It's pointed out straight away that there is no way for science to cause an eclipse early, only powerful magic can do that. It's unclear if the moon is actually being moved out of position or if it just looks like it is. It's also implied that the reason Kara is losing her powers so fast is because of the magical nature of the eclipse. Notably Mon-El, who also gains his powers from sunlight but is not Kryptonian, is unaffected.
- Beam-O-War:
- Kara and Reign engage in an Eye Beams version during the fight in the Fortress. Thanks to the eclipse becoming total, Kara loses her powers and Reign wins.
- Alex tests her new gun against Purity's scream, causing an explosion which knocks them both out.
- Big "NO!": By Reign, as Purity and Pestilence are killing one another.
- Brought Down to Normal: Supergirl loses her powers while in the mind valley, then again at the Fortress of Sanctuary once the eclipse reaches totality.
- Cliffhanger: Reign setting out to kill Ruby in order to secure control over Sam's body.
- Collapsing Lair: The Fortress of Sanctuary dissolves into nothing after Purity and Pestilence are killed.
- Conflicting Loyalty: Supergirl asks James to break into Lena's labs as Guardian and confirm whether or not there is any Kryptonite left. James is clearly uncomfortable with going behind Lena's back, as he still has feelings for her. In the end, he aborts the mission.
- "Freaky Friday" Flip: Sam does this to herself, by taking control of Reign's body for a brief amount of time. Unfortunately, this also means that Reign takes control of Sam's body in Juru, giving her free reign to hurt the protagonists.
- Friendship Moment: At the end of the episode Kara admits that she overreacted about Lena having Kryptonite and asks for a clean slate.
- Fusion Dance: When Purity and Pestilence are killed, their essence leaves their bodies and joins with Reign.
- Get A Hold Of Yourself Man: Villainous example. The second Pestilence recognizes Sam taking over the body from Reign, she punches her, which causes Reign to gain back control.
- Heroic Willpower: Julia and (briefly) Sam are able to overpower their World Killer personalities and take back control of their bodies.
- Hypocrite: Lena points out that Kara is being one by lecturing her about keeping secrets:
- To a lesser degree, Lena also calls out Alex on keeping her own secret about working for the DEO.
- "I Know You're in There Somewhere" Fight: Alex toward Purity. Thankfully, Julia is able to break out in the end.
- Instant Expert: Lena is able to pilot the Legion ship without any prior training or even knowledge of the craft, to Brainiac's surprise.
- Internal Reveal:
- Lena learns that James is Guardian.
- Averted by Supergirl, who declines (despite given an opportunity) to reveal to Lena her real identity.
- Jumped at the Call: A villainous example. When told that they must purge their human selves to fully become World Killers, Pestilence doesn't hesitate to sever whatever metaphysical lifeline was keeping Grace breathing.
- Mutual Kill: Pestilence fatally stabs Julia, who uses Purity's powers to vibrate Pestilence to death.
- No Good Deed Goes Unpunished: Lena's attempts to help Sam backfired big time. All she wanted to do was prove she wasn't "another Luthor".
- Note to Self: Sam and Julia carve everything they can remember of their lives into the rocks around them so they won't forget who they are.
- Nothing Personal: What Lena claims her private Kryptonite supplies to be toward Supergirl. Alex responds that Kryptonite is very personal to Kara for obvious reasons.
- Offing the Offspring: The episode ends on a cliffhanger showing Reign being told to kill Ruby.
- Psychological Torment Zone: The valley tries to drive Sam and Julia insane, showing them the victims of their World Killer selves while their memories of all they know and love are slowly erased. They manage to resist with some help from Supergirl, Alex, and Lena.
- Sarcasm-Blind: Brainy. When he tells Kara, Lena and Alex that the chances of them getting hurt in the foreign dimension are above 50%, Alex sarcastically states how reassuring that is. Brainy doesn't get it and says that it isn't.
- Split-Personality Takeover: In order to fully become the World Killers, Reign, Purity, and Pestilence have to kill off their human personalities. This is easy for Pestilence, since Grace was already on-board with the idea, but Sam and Julia are able to retain their sense of self and eventually regain control, if only briefly.
- Summon to Hand: Winn built Alex's new outfit with magnetic palm pads designed to draw her gun back if she drops it. Hilarity Ensues when it rips Brainiac 5's Legion ring right off his finger.
- Takes One to Kill One: Reign boasts that only a being as strong as her can hope to kill her. Julia, after taking over control from Purity, realizes that she has the power to kill the other World Killers and does so with Pestilence, though Pestilence kills her in turn.
- Total Eclipse of the Plot: The World Killers cause an eclipse during their ritual to purge their human selves, which will eventually have the side effect of ending all life on the planet. Stopping them before the eclipse is complete and Supergirl is rendered powerless becomes vitally important. (It is also briefly stated that the eclipse will cause a major temperature decrease.)
- What the Hell, Hero?:
- Supergirl and the DEO give Lena the third degree for her secret experiments on Sam and not telling them she was Reign, as well as her possession of Kryptonite. Lena counters that she doesn't answer to them.
- Lena in turn points out that Supergirl has secrets of her own, namely her secret identity, so she's hardly in a position to criticize Lena for having some. She also says something similar to Alex regarding the latter's involvement with the DEO.
- What You Are in the Dark: James chooses not to break into Lena's vault and lies to Winn that he did and found it empty. He later comes clean to Lena herself.
- Wham Line:Lena: That wasn't Lex's Kryptonite. I figured out how to make it.
- Witch with a Capital "B": Julia calling Pestilence a witch certainly comes off as this.
