Board Thread:Spoilers!/@comment-26443838-20160105035933/@comment-6175354-20160106190644

CoolDudeAl wrote: They rarely do episodes that are split equally 3 ways. And we already know that Zelena in Oz with Dorothy is some of the episode, and Zelena and Belle in SB is some of the episode. So either they are doing just a tease of the Underworld's SB, or somehow they are connecting Zelena and Belle to the rest of the cast. Exactly.... the only time OUaT did something like that, was in 2.05.

With 5.15 being the Hook-centric episode; I am inclined to believe, that Belle and Zelena are somehow reopening the portal to the Underworld. Adam and Eddy already confirmed, that the character are not spending the entirety of 5.B down there.