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Your Worst Nightmare Will Return In The 'Pretty Little Liars' Christmas Special

Plus, find out which Liar boyfriend will don a pair of tights!

The ladies of "Pretty Little Liars" have been terrorized by a plethora of humans, animals, and text messages over the years, but producer I. Marlene King just confirmed to MTV News that the most terrifying nightmare of all will return to haunt the ladies for next week's Christmas special, "How the 'A' Stole Christmas."

"We haven’t seen the last of that zombie baby mask," King told us over the phone. "That zombie baby mask makes a special appearance in the episode."

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That's right -- the creepy, anonymous murder-stalker that first appeared in "The First Secret" will return for the big December 9 midseason special, which will mostly focus on the Liars spreading holiday cheer after Mona's (Janel Parrish) death and Spencer's (Troian Bellisario) arrest.

"Mona left a plan behind in case of her demise, and that plan is delivered to Hanna at the beginning of the episode," King explained. "It gives them, especially Emily -- the Pretty Little Liar who loves Christmas the most -- hope that maybe they can give Spencer a Christmas."

Fans will remember that when Mona bit the big one in "Taking This One to the Grave" last fall, she had just figured out who actually murdered Bethany Young -- and everybody's money is on the fact that it was Alison (Sasha Pieterse). When we meet the Liars again, Mona's ghost will revisit Alison for a rift on a Charles Dickens classic, with a little bit of Alfred Hitchcock thrown in for good measure.

"Last we saw Toby, he had a terrible car accident, and [now] his leg is in a cast and he’s in a wheelchair," King continued. "This episode is 'A Christmas Carol' meets 'Rear Window.' We do a very classic homage to Hitchcock’s brilliant thriller, and Toby is our Jimmy Stewart."

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For those unfamiliar with the classic film, this means that Toby will try to solve the mystery of Mona's death (and his girlfriend's arrest) from afar, but King says that the ladies of the show will join in on the murderous fun as well.

Related: The Last ‘Pretty Little Liars’ Book Is Out — And We’ve Got A Peek

"When we start the episode, the Pretty Little Liars make it pretty clear that they feel that Alison had something to do with Mona’s death," she said. "It’s the ultimate betrayal. We find them at the beginning of the episode completely estranged from Alison... the show is definitely beautiful, and cinematic and festive and merry ho-ho, but at the same time, it is scary and thrilling and horrific at times."

Sounds like the "Pretty Little Liars" we've grown to know and love over the years, no? But for those who don't necessarily want their holiday season to be filled with murder and mayhem, know that there is always a silver lining -- and this time around, it features tights.

"Caleb is the best boyfriend in the world," King concluded. "He shows up in tights and an elf costume to help Hanna at a church event."