It took six seasons but Once Upon a Time finally reached its full Disney potential with an enchanting musical episode.

"A Song in Your Heart" not only serves as the ABC drama's first foray into the musical realm, but is the penultimate episode for a season that could end up being the show's last if the network chooses not to pick it up for another run. That means Once not only had to balance creating original music and a suitable plot, but move the story forward while simultaneously setting up an eventful finale. Considering the pressure Once and its cast and crew were under, they did a stunning job of mixing fairy tale magic and raising their stakes for next week's two-hour event.

The singing began in a flashback to the Enchanted Forest on the night of Snow and Charming's wedding. Distraught over the threat of the Evil Queen's (Lana Parrilla) curse, Snow (Ginnifer Goodwin) made a wish that put a song in everyone's heart — giving them the power they'd need to defeat the queen and give Emma (Jennifer Morrison) a chance at a happy ending. The music wasn't able to take down Regina's alter-ego, but the songs were stored in Emma's heart for when she would need it.

Once Upon a Time: Ginnifer Goodwin and Josh Dallas Go Full Disney for Musical Episode

Back in Storybrooke, Emma was able to finally unleash the song from her own heart just in time to thwart the Black Fairy (Jamie Murray) from taking away everyone that Emma loves. That gave everyone enough time to come together for Emma and Hook's fairy tale wedding, but it also put them in the middle of town for when the Black Fairy's own evil curse cascaded over them. The charming musical ended with a cloud of Black Fairy dust covering the people of Storybrooke and taking them to a time and place unknown for the Final Battle. got the chance to talk to Once stars Ginnifer Goodwin and Josh Dallas about the events of the musical episode and what fans can expect for Snow, Charming and Emma in next week's showdown.

Ginnifer Goodwin and Josh Dallas, <em>Once Upon a Time</em>Ginnifer Goodwin and Josh Dallas, Once Upon a Time

How many takes [did it take to get Charming's entrance right] and how did [Ginnifer] keep a straight face?

Josh Dallas: She never kept a straight face.

Ginnifer Goodwin: It wasn't that it wasn't straight. There was a choice I made through most takes which was I ...

Dallas: Wasn't going to look at me?

Goodwin: No! What?! You were there!...My first choice was that when he comes in I get a little hot under the collar from his singing. And I feel you can see me kind of blurry in one of the angles going 'ohhhhh...' [fans self] and they didn't feel that that worked for the storyline of the actual song. So, I was asked to keep on the track of "Why are we singing? Oh yes, I walked off the balcony last night and made this wish." I did a hundred takes of "Oh, me. Who knew?"

Dallas: I didn't even know! He was so self-involved with his own voice. He just loved the way he sounded.

Goodwin: [Josh] practiced that a lot at home.

At the end of this episode, it's fade to black. The curse has hit. What can you tease about what we're going to see in the finale?

Dallas: The final battle. The final battle that we have been waiting for it is going to be a...what is it going to be?

Goodwin: Epic!

Dallas: Epic! It's going to be a showdown of epic proportions. That is for sure.

Can you say where?

Goodwin: Storybrooke. That's where it is geographically. Emotionally, they are all over the map. Main Street more specifically.

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We've seen so many curses on this show. How does the Black Fairy finale curse compare? What was your reaction when you learned what it does?

Goodwin: The breaking of the curse involves something far more dramatic than anything that's ever broken a curse before. If it were to break! I am not saying it breaks! We could all just be blown into oblivion and that's just it.

Emma just used the power of song to stop your evil villain. How can you top that in the finale?

Goodwin: What broke the very first season's curse was the kiss, a very pure unromantic true love expressed between mother and son. The love that it takes in the finale in order to do what has to be done to break the curse, I feel is categorically bigger.

Because the show hasn't gotten a pickup yet, if this is the final episode — if it's the series finale instead of the season finale — will fans be happy with how it ends?

Goodwin: I think so.

Dallas: I think most people will be. You can't please everybody. I think that some people will be happy and some people will be angry and upset...They've honored these characters and this part of the story, this part of their journeys. I think each character gets something that the fans should be happy with, that each character deserves.

Goodwin: I think they found a magical way to make it go either way.

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Once the Black Fairy curse hits, is everybody on the same page, or are forces dividing our heroes? Are people working together or are they split?

Dallas: I think everybody's working together.

Goodwin: It's togethery. That's the scientific word.

Dallas: It's the only way. It's the only way to defeat it. And also what you saw in this episode was the gift of song that Emma got was her voice, having that song in her heart, she knows that she's not alone. So I think that togetherness goes through until the finale.

Without spoiling the finale obviously, if this is the last episode, how do you feel about where your characters end up? Do you feel like you have closure on the characters?

Dallas: Yeah, if it's the last episode, I would be satisfied.

Goodwin: I really feel that what they've done, because we don't know, it's kind of shocking how well they created something open-ended that could be seen as — I mean in classic Once Upon A Time style, there is a twist. The twist means that it could go either way, and it serves all of the characters very well.

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How about for Emma though? Since this episode is her happy beginning, how do you think it might end for her character?

Goodwin: Well, she is involved in — because she's half of the Final Battle — she's involved in the epic decision that may or may not break the curse. I don't think that the scenarios could have been flipped. I don't think that the wedding as the final episode of the season would have been as satisfying as what is to come for Emma. It's a really good storyline.

Are you guys aware of any plans for Season 7? Do you see where the story could go if you get the pick up?

Goodwin: Oh, for sure. They definitely have great ideas about what could happen should we go on, and I'm just kind of assuming it's going to go on. Like forever.

Come back to after the West Coast airing to see what show creators Adam Horowitz and Eddy Kitsis have to say about the musical and what's in store for the characters in the Final Battle.

Once Upon a Time's two-hour Season 6 finale airs Sunday, March 14 at 7/6c on ABC.