Elizabeth Mitchell Elizabeth Mitchell

Curses are a dime a dozen in the fractured fairy-tale world of Once Upon a Time — but this one's a doozy! This Sunday's episode finds Ingrid, the crazed Snow Queen (Elizabeth Mitchell), all set to devastate the citizens of Storybrooke with her Spell of Shattered Sight.

"It's much more emotional and apocalyptic than the other curses on our show where we're just killing people," says cocreator Edward Kitsis. "This is a rage curse — fun and scary at the same time —t hat can bring out the worst in everyone. If it isn't stopped, it will make our characters turn on each other in horrible ways." Longtime friendships will be threatened. So will romances.

"We beta-tested the curse in Episode 8 [Nov. 16] when we got to see how terribly it affected Anna [Elizabeth Lail], who is the nicest, lightest, most spirited character you can find," says cocreator Adam Horowitz. "So just imagine the curse's effect on those who we know have a dark side, like our Evil Queen [Regina, played by Lana Parrilla]." Adds Kitsis: "Even a hero like Snow White [Ginnifer Goodwin] has a bit of darkness she'd never dream of acting on — but the curse will reveal it."

Only Elsa (Georgina Haig) and Emma (Jennifer Morrison) are immune to all this — the former is the Snow Queen's niece; the latter was raised by the Snow Queen as a foster child — so it's up to them to save the town. Meanwhile, Elsa's saga in Storybrooke and Anna's parallel story in Arendelle are "headed toward a collision in our winter finale [Dec. 14]," Horowitz says.

So, will that be a wrap for all this Frozen stuff on the series? The showrunners can't quite let it go, let it go. "The arc will come to an end and the Snow Queen is dealt with, but something surprising rears its head in the aftermath of this story, and it takes us right into our next arc," Kitsis says. "It's our favorite twist yet."

Once Upon a Time airs Sundays at 8/7c on ABC.

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