If you're wondering whether Supergirl will have an equal part in the next crossover, the answer, according to producers Jessica Queller and Roberto Aguirre-Sacasa and every cast member I talked to at the show's SDCC, is a resounding yes.
First off, if you're wondering, Cat Grant will be back in the season premiere, but things will definitely be different. Jimmy (Mehcad Brooks) is in charge at CatCo, which is giving him more of a chance to be an adult and take on greater responsibility. But Brooks also hinted at an impending shakeup (is that part of Cat's return?) and a love interest down the road.
He also says we'll see more Guardian, which is good, considering the training he's done and the "eleventy billion fittings" for the costume.
We also learned that Mon-El will be back. Actor Chris Wood said, “I'm here. That should tell you something.” The producers also confirmed his return, which will be interesting, considering the place Kara will be in when Season 3 begins.
Melissa Benoist gave us an idea of where Kara is mentally and emotionally, namely that she'll be very impacted by the loss of Mon-el. Kara has thrown herself into being a hero to keep busy and not think about the loss of Mon-el. She's withdrawn into herself and in a darker place, but also in a more adult place. In fact, the season overall will be questioning what is it to be human, and it sounds like all Kara's relationships will face changes.
We also discussed what the cast members want to see from their characters, and unearthed a few tidbits from them.
Jeremy Jordan is interested in seeing the friendship with Kara rebuilt, and his relationship with Lyra will continue. He also thinks we'll see more of his backstory. Mehcad Brooks also says he hopes for more backstory, and he's especially curious to know what Superman will think of him being Guardian.
Katie McGrath is hoping to interact with more of the cast, and she's definitely aware that parts of the fandom would like to see more happen between Lena and Kara. While she says it's not something that's happening as far as she knows, she loves the chance to play anything, so if it goes that way, then there ya go. Overall she's just really happy to be here. She did warn that, while people expect her to go dark and carry on that aspect of the Luthor dynasty, she's not so sure. “Who’s to know, she may end up the savior of National City.”
We also learned that there are more characters in store for David Harewood. He says we should definitely keep an eye out for Episode 3.
Our big unknown right now is Odette Annabelle's Reign, but she promises that, while she may be a world killer who's been bioengineered in a lab, she's different than other villains we've seen because she's not bent on world domination or destroying the planet; she has very specific goals. We don't know what those goals are, but she's excited about sharing this meaningful, strong, and "heartbreaking tale."
We also know we'll see a a big confrontation between Reign and Supergirl down the road.
One more thing, in regard to the series crossover, it'll start on Supergirl sometime next September.