From the moment I became aware that Odette Annable's character Samantha Arias was actually the villainous Worldkiller Reign, I had a feeling that this might be Supergirl's best foe yet. Unlike the masked-villain-who-turns-out-to-be-a-friend thing we've seen done to death elsewhere in the Arrow-verse, we knew from the very start that Sam was eventually going to turn into Reign. It made her interactions with the core cast -- Kara, Alex, and Lena -- and her friendships with each that much more fraught with tension. How will they react once she is unmasked is now a more interesting question than how we will react (because it almost never lives up to our guesses).

There have been some complaints that this year Supergirl has gone too dark. Kara has spent most of the season so far grieving for Mon-El, and now, almost wishing he was gone rather than seeing him there with a new love. Alex and Maggie's breakup was painful, and there were even a few episodes devoted to the genocide that J'onn's people suffered at the hands of the White Martians. And yes, while Supergirl (and the character of Kara in particular) works best when there's more positivity, the show (and Melissa Benoist) has handled this darker turn well by actually leaning in to the stakes -- physical and emotional -- that the catalysts of this season's darkness brings.

One of the best things about the final fight between Kara and Reign in the midseason finale, "Reign," was that Kara went into this fight in an emotionally difficult place. Though Alex reverses her advice and tells Kara to go full, emotionless Kryptonian in the wake of Mon-El's return, she is still extremely heartbroken over everything that has happened with that relationship. She is not at her strongest, and Reign -- who matches Kara's base strength -- has an easy time besting her. There was something really, really intensely dark about seeing Kara bloodied and broken by Reign. We've never seen her this physically and emotionally battered. To leave the season there though (until it returns this winter) creates the opportunity for Kara to heal and come back stronger than ever.

But Kara's not ready to march back into health and positivity just yet; Reign's identity as Sam is still a mystery to her. That reveal will surely also be devastating for Kara, who already feels so burned for trusting in Mon-El. To discover that her friend Sam is her greatest adversary will be a huge blow. And yet, as much as I like how Sam/Reign has been developed this season, her transformation felt too sudden. To have her Worldkiller self take over and make her evil is not as powerful as having Sam choose to embrace that side of herself. That's a more devastating narrative to explore, and one where Ruby would surely play a pivotal role. What makes Sam human, and ultimately kept her from turning into Worldkiller fully (until now) is her love for Ruby. In those final moments of "Reign," we see Ruby running into see her mother on Christmas, only for Sam to turn sharply, fighting her Worldkiller mode. We don't see her face, which is terrifying, but it's also the perfect place to leave it. She's still in between her human self and her Kryptonian self -- the same way Kara is.

The best villains of the Arrow-verse have been dark inversions of the heroes: Reverse-Flash / Wellsobard on The Flash, Prometheus on Arrow, and the Legion of Doom to counter the Legends of Tomorrow. Reign is also from Krypton, has immense powers, but acts as the "devil" to Kara's savior. Some of the mythology we get in this episode follows the Bible, with the mark of the beast and the coming of judgement day. The Superman motif has never been shy about equating its alien hero with the savior Jesus Christ, and Supergirl keeps some faint shadow of that here. But the real point is that it deals elementally with good versus evil. To complicate that, as Kara has embraced her human side, she has faltered in her alien side. That balance is surely what the rest of this season will focus on.

For now, Supergirl has handled this year's villain and her rise exceptionally well (other than my note on her choosing her destiny, which could still happen), and kept some of its jolly nature despite these dark times. Most of "Reign" was a delight, from the Christmas parties to Jimmy and Lena's growing attraction to each other, to J'onn and his father discussing hot cocoa (and Hall and Oates!) There's still plenty of light in Supergirl -- but Supergirl herself needs to find a way to it again as Reign continues to challenge her.

Supergirl will return Monday, January 15th on The CW.