Reign, Legion of Super-Heroes, and a Love Triangle in 'Supergirl' Midseason Finale Featurette

The CW has released a featurette for "Reign", tonight's midseason finale of Supergirl's third season.

The episode will see Samantha Arias (Odette Annable) fully embracing her Reign persona, including leaving mysterious symbols all throughout National City.

"This mark mysteriously starts appearing all over National City." executive producer Robert Rovner says in the featurette. "It begins in a crop circle-y kind of way. And so everybody is kind of freaked out, and wondering who's making the mark."

Kara Danvers/Supergirl (Melissa Benoist) ends up potentially finding answers in an interesting place - Thomas Coville (Chad Lowe) the Church of Rao preacher (and potential stand-in for Gog) seen earlier this season.

"We see the reappearance of Thomas Coville, [played by] Chad Lowe, who was amazing in 'The Faithful' episode, reappear." Rovner explains. "And he thinks he understands what the markings are about. He thinks that they're a prophecy about the end of days, and what it means for Supergirl."

"From ancient Kryptonian lore," adds executive producer Jessica Queller.

Meanwhile, Kara will be dealing with the recent arrival of Mon-El (Chris Wood) and his wife from the future, Imra Ardeen/Saturn Girl (Amy Jackson). And while last week's "Crisis on Earth-X" crossover made Kara gain some perspective, she will apparently still be uncomfortable about the arrangement.

"Kara is still very much grappling with the fact that Mon-El has reappeared, with this beautiful lovely wife, named Imra." Queller revealed. "We really have three good people - Imra, Mon-El, and Kara - stuck in this untenable situation."

Could Imra actually be brainwashing Mon-El in the process? Supergirl fans will just have to stay tuned to find out.

Supergirl airs Mondays at 8/7c on The CW.