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'The Flash' Star Danielle Panabaker On Tonight's 'Terrifying' Finale

Plus, she reveals who she 'ships most with Caitlin!

Tonight's (December 9) mid-season finale of "The Flash" is the biggest episode yet -- and not just because Barry (Grant Gustin) finally comes face to face with "The Man In The Yellow Suit."

It's because Caitlin Snow (Danielle Panabaker) also meets up with a ghost from her past... Specifically, her fiancé Ronnie Raymond (guest star Robbie Amell), who seemed to have died in the particle accelerator accident that kicked off the show. As viewers know, however, the accident gave him some fiery superpowers, not death.

So while Barry is dealing with the man who may have killed his mother, Caitlin is dealing with emotional trauma of her own.

"She thinks she's going crazy!" Panabaker told MTV News over the phone. "She's trying to understand what is going on, and figure out who Ronnie is now."

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Comic book readers (and promo watchers) know that Ronnie is turning into the future hero known as Firestorm, a man able to change the chemical formula of matter at will. But given that every super-powered metahuman on "The Flash" has gone a little bit mad from the power, minus The Flash himself, Caitlin is going to be a little too busy to help Barry with his own problems.

"There's so much about Reverse Flash that is so scary for Barry," Panabaker continued. "The fact he has a similar power, but probably with more experience, is terrifying. And the Reverse Flash... He is a bad guy, and Barry is only still getting his footing in trying to figure out how to use his powers best."

By the end of the episode, viewers still won't know the identity of the villainous Reverse Flash; and according to Panabaker, the cast isn't entirely sure, either.

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"They tell us things, but as the season evolves, these storylines are evolving too," Panabaker said. "Even from the pilot, the initial plans they had for all the different characters changed a little bit. The actors start to embody the roles, so we had an inkling of an idea, but you never know... Things can always change."

Part of those plans? That Caitlin Snow would reach her own comic book destiny, to become the ice-powered Killer Frost. When Panabaker described her character to us as initially "cold," but "warming up" over the course of the season, we had to call her out and ask about whether Killer Frost was still in the cards.

"That is something that is still in her future, absolutely," Panabaker said. "But right now it’s still exciting to be a part of Team Flash."

In the immediate future, though, Caitlin will be dealing with the figurative and literal fall-out from Ronnie's return... Something that might put a crimp in SnowBarry shippers' fondest dreams.

"I would say, stay tuned! There is so much love between Caitlin and Ronnie, and I feel like the next few episodes you start to get to see that," Panabaker said when asked what she would tell fans who 'ship Barry and Caitlin. "It’s almost a story book love story, and it’s devastating when he gets taken from her -- but you know, once he's back in her life, you never know what can happen."

Though Panabaker is aware of the SnowBarry faction, she instead harbors a secret love for another 'shipper group: Caitlicity, or those fans who 'ship Caitlin and her "Arrow" opposite, Felicity Smoak (Emily Bett Rickards).

"How cool is it that, there are such strong women and female characters on television every day?" Panabaker said. "Thanks to Marc [Guggenheim] and kicking ass! I love it!"

And while we may never get to see that particular pairing on TV... We also probably won't get to see a musical episode any time soon. Though co-stars Tom Cavanagh and Carlos Valdes recently released a musical holiday card, and Jesse L. Martin is an insanely accomplished musical theater actor, Panabaker deferred, saying she has, "zero musical talent."

That said, though a musical episode isn't in the future, there is, "some karaoke-ing" according to Panabaker. Still, don't expect Caitlin Snow to belt out songs from "Frozen."

"My go-to karaoke is sitting back and applauding everyone else!" Panabaker said laughing.