Elizabeth Mitchell of "Lost" will be joining the cast of "Once Upon a Time" for Season 4. There is no word on what role she will play. Word is that she will be in an arc that covers several episodes and which involves the characters from "Frozen."
Mitchell also has starred in ABC’s "V" and was most recently on NBC’s "Revolution."
The "Frozen" sisters Anna (newcomer Elizabeth Lail) and Elsa ("Fringe" familiar Georgina Haig) will be major factors in Season Four. The events in Once Upon are expected to take place after the events in last year’s animated Disney hit, so Anna and Elsa will be working together but ironing out whatever personal differences between them that remain. Prince Hal will be gone, Kristoff will be around with his reindeer (at least we hope the reindeer is around!), and so on and so forth.
Advance word is that Mitchell will play (what else) a villainess of some kind. On tv, you can't have "good" (Anna and Elsa) without having someone "bad" that they fight against. Recall that Hans Christian Anderson's original "The Snow Queen" was about a malevolent witch, a factor the Disney film completely ignored (everything involved here is a Disney product).
The "Once Upon a Time" version of "Frozen" is going to require some kind of opponent to Anna and Elsa, because, as everyone knows, you can't bring over fan favorites from somewhere else on a continuing basis and then turn them into unlikeable characters. That just doesn't work on tv.
Think of the children! All those kids waiting on line in Disney World at Princess Fairytale Hall to meet their idols from "Frozen"! Elsa or Anna unlikeable? Oh the horror!
Can't damage that golden brand, no sirreee.
Much better to make Anna and Elsa (and Kristoff, who sounds as though he is going to be a helpful idiot in that "idiot savant" way that tv does so well) "good guys" and then bring in someone like Mitchell to "stir the pot" and give them plenty of chances to show how wonderful they really are. Probably Mitchell's character will be related to Anna and Elsa in some fashion and they have childhood traumas to sort out, that's the tv version of real life. Sort of like the "Wizard of Oz" storyline from Season Three, with all the fun flowing from the Evil Witch of the West battling Regina.
That's just a guess, everyone is going to speculate, but it's how tv series usually work. We'll see soon enough.