Credit: Video Still

One of the more chilling images from the Pretty Little Liars Season 4 Halloween episode (Season 4, Episode 13) promo is that of someone dressed up in a gas mask suit, which we first spotted in "A"'s Lair in the summer finale. Something about gas masks are just so darn creepy!

In this clip from the episode, the gas mask person appears to be following Hanna, and we see that he or she has donned those classic "A" team gloves. The implication is that we should be afraid, very afraid of this masked mystery man or woman.

Who's the person behind the mask this time? We'll theoretically find out tomorrow (though we supposed "Who's the Person in the Gas Mask?" could become the new "Who's the Queen of Hearts?"), but that still leaves us some time to speculate.

So, here are our best guesses about who might be stalking the Liars through Ravenswood wearing one very disturbing costume.

Ezra. This is the obvious answer. We saw the gas mask in "A"'s lair, we saw Ezra in "A"'s lair...put two and two together, and you've got creepy EzrA stalking the Liars in the world's most frightening costume. That said, based on the promo we know that a non-masked Ezra appears in the episode at some point. Obviously that doesn't exclude him from being the one behind the mask (and he is in military gear at some point), but it does make us less confident that he's the one behind the mask.

Luke. Luke is a new character from Ravenswood, but that doesn't exclude him from appearing in the Halloween episode, and we know he is, like Ezra and the gas mask wearer, dressed in military gear. Plus, this script spoiler hints that the Liars will find themselves suspecting someone they've never met before of being "A". Maybe it's because they see Luke wearing the gas mask.

Wren. We still don't trust Wren, and we're not sure what he's up to at this exact moment on the show. He could totally be stalking the Liars. This could also be true of Jenna (depending on how her eyesight is at the moment) or even Melissa, but Wren seems the most likely suspect from their group.

Ali. At this point, most fans assume Ali is alive, and is Red Coat. While we agree that those are both probably true statements, nothing says she has to wear the red coat all the time. We know she's afraid of "A"; maybe she decides to disguise herself with "A"'s own gas mask to create maximum confusion.

Who do you think is behind the mask? Sound off in the comments below!

Catch the Pretty Little Liars Season 4 Halloween special on Tuesday, October 22, 2013 at 8 p.m. ET on ABC Family.

Rebecca Martin is an Associate Editor at Wetpaint Entertainment and our resident Game of Thrones, Breaking Bad, and genre TV expert. Follow her on Twitter and Google+!