So, what can we expect as Zelena moves forward with her dastardly plot? We've taken a closer look at the promo to see what it reveals.
1. Time to start killing? The promo opens with Zelena saying she may have to start "killing people." Uh-uh. If she's willing to resort to murder, everyone is in trouble.
2. Flashback to the lost year. At :05 we see that we'll finally learn more about what went down between the Wicked Witch and our heroes during the lost year, with Aurora warning the Charmings that the witch is after their baby. It also looks like Zelena and Snow had a run in during that year, which we get a hint of at :09.
3. Glinda! This episode will also introduce Glinda, the good witch. It looks like Charming and Snow seek her out at :11, as part of the flashback. Bad news, though: Glinda says even her powers can't stop Zelena.
4. Fire! We're not sure what the fire filled doorway at :14 is all about, but we're going to go ahead and guess it's nothing good.
5. Attack of the flying monkey. At :15 a flying monkey attacks Hook, Smee, and... Henry. How's Emma going to explain that?
6. Charming collapses. In the past, Charming collapses while Snow (is it Snow?) appears to be working some sort of spell at :17.
7. Henry in danger! Forget explaining the flying monkey, actually — Emma's going to have to explain why a crazy witch is threatening Henry's life at :18... assuming he makes it out alive.
8. More Zelena and Regina. It looks like we'll be treated to another Zelena and Regina confrontation in the past, with Zelena telling her sis, "this is how you take away a happy ending" at :20.
Check it out for yourself.
Did we miss anything important? Interpret something wrong? Let us know your thoughts in the comments below!
Catch the next episode of Once Upon a Time on Sunday, April 27 at 8 p.m. ET on ABC.
Rebecca Martin is an Associate Editor at Wetpaint Entertainment and our resident Game of Thrones, Pretty Little Liars, and genre TV expert. Follow her on Twitter and Google+!