Once Upon A Time Season 4 finale
Emma will reunite with her childhood friend Lilly in episode 20OnceUponATime/Facebook

Once Upon A Time is just two episodes away from the finale, as the line between heroes and villains becomes faint.

In episode 19 titled Sympathy For The De Vil, Emma reaches the end of her battle between light and darkness.

In the episode, Emma shows no sympathy for Cruella de Vil when the dog whisperer holds Henry hostage, and she even shoves the villain off the cliff.

Charming and Snow White try warning their daughter that Cruella cannot kill anyone, as the last thing the author wrote about her was "Cruella de Vil can no longer take away the life of another."

But Emma blasts Cruella off a cliff to her death to save Henry from being shot, thereby embracing her dark side.

The new episode next week is titled Lilly, which will feature the reunion between long-lost friends Emma and Lilly, who we learn is Maleficent's daughter.

Episode 20's official synopsis reads: "Emma's potential for darkness is looming over everyone, but when Emma realizes Maleficent's daughter Lily is in fact her closest friend from her foster care days, she resolves to find Lily and reunite her with her mother."

Regina joins forces with Emma and together they set out to track down Lily and to warn Robin about Zelena. However, neither of them is prepared for the harsh realities they will encounter in the outside world.

Meanwhile, in Storybrooke, "Gold faces a crisis involving Belle. In a foster care flashback, things are looking up for young Emma with her new family until Lily's appearance threatens to destabilize everything."

A new promo shows a weird magical blue smoke voicing, "The girls fate remain intertwined, as they always were and always will be," while shots of a young Emma and Lilly in foster care are shown.

The voice over says, "Fate bought them together once, now they are re-united, as mortal enemies."

"She wants revenge," says Emma, as Lilly claims, "Your parents deserve to be punished," and
the promo ends with the two fighting each other.

Executive producers Adam Horowitz and Eddy Kitsis preview episode 20 and discuss what to expect in the finale.

Adam Horowitz told Tvline, "The cold-blooded killing of Cruella, coupled with her riff with the 'rents, make for an ever-unseemly Savior."

The reverberations of Emma's dark action become the driving force for what happens in the next two episodes followed by the two-hour finale, says the producer.

"Emma has crossed a line," he says. In the 26 April episode Lily, Emma reconnects with her childhood friend (played by Agnes Bruckner), who viewers know is Maleficent's "lost" daughter. That reunion, however, "is not all deathly conflict," Horowitz noted.

Eddy Kitsis added, "There are moments of warmth, and there are moments of bonding. And there's a lot of emotion. It's a real story of friendship."

The producer teased about what might happen in the season 4 finale.

"We make good on what Regina was after, in the sense that she wanted to find the Author and have him rewrite endings," Kitsis shared.

But compared to recent finales, "Nobody is coming out of an urn and freezing people," Horowitz said.

"Usually we're like, 'Hey, we're going to a new land,' but this is much more in the vein of when Gold looked up [at the end of Season 1] and said, 'Magic is coming,' where a condition on the show changed as opposed to the characters changing," Kitsis added.

There is a great potential that Emma will turn dark in the season 4 finale.

Watch Once Upon A Time episode 20 on 26 April at 8pm on ABC.