This fall, expect to see some Reign on Supergirl. The villainess made her grand debut in the Season 2 finale, where she was introduced as another baby saved from the destruction of Krypton. However, when Season 3, Reign will be fully grown -- and she'll soon become a thorn in Supergirl's side. At Comic-Con International in San Diego, Reign actress Odette Annable shared new details about her character and her "very specific agenda."

"Reign, as most of you know probably, she's a Worldkiller. She was bioengineered in a lab. She was sent from Krypton much like Kara and Clark, but her story is going to be different than any other villain that you've seen on Supergirl Seasons 1 and 2, mostly because she doesn't come to Earth to go on a killing spree," Annable revealed. "She has a very specific agenda that she is out to do, and you will see that story unfold throughout the season. For me, it's really amazing because it's kind of a heartbreaking story and I think that you'll feel for her."

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Asked if Reign's struggle could be a question of nature vs. nurture, she said, "Potentially, yes. I think that we're gearing this season to share the story of humanity, really. With Reign, I think that that's a big part of it."

"We just started shooting, and so I have a whole year to discover her and so I think it's nice that I don't know much. In the comics, we don't really know much about Reign," she explained. "It's very sort of a surface-level, and I think that what Andrew Kreisberg and Greg Berlanti are good at… They're going to take bits and nods from the original character but also make their own character, and so I feel like the pressure is off a little bit in that way, where I can really dive in create something. I can be an artist in that way, and not stick to something that we've seen... I really want to get this character right. I think it's a really great character and a great story to tell."

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Executive producer Robert Rovner also offered his perspective on the character and what sets her apart from other Arrowverse villains. "Well, I think Reign saw her genesis in the season finale, as she was sent in her own pod towards Earth. She's a Worldkiller, genetically engineered, and so she's I think a very different villain than any of the other villains on the other Arrowverse shows," he explained. "She comes with her own agenda that's going to put her at odds with Supergirl."

"We're so excited about the casting of Odette Annable and we feel like this going to be a villain that the audience emotionally invests in and that's something very special. It's going to be amazing," added executive producer Jessica Queller.

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Annable also shared what it was like to play a female villain, calling it "badass! I feel like a badass mf! No, it's really all fun, and I've done some fighting and stunt training before, and I really enjoy that rush. I don't get into the gym otherwise, so this is a great reason. If only for that, then I'm in."

Returning to The CW on Monday, October 9th at 8 p.m. ET/PT, 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.