Board Thread:Spoilers!/@comment-25733960-20161205025332/@comment-30345232-20170304151932

 What can you say about Gideon, and is his story a purposeful dark <span class="IL_AD" id="IL_AD3" style="box-sizing:border-box;position:static;border-bottom-width:1px!important;border-bottom-style:solid!important;border-bottom-color:rgb(221,60,66)!important;text-decoration:underline!important;color:rgb(221,60,66)!important;background-image:none!important;background-attachment:scroll!important;cursor:pointer!important;display:inline!important;padding-bottom:1px!important;float:none!important;font-weight:bold!important;font-style:normal!important;background-position:0%50%!important;background-repeat:repeatrepeat!important;">mirror  to Emma’s backstory?

 EK:  It is in a certain way. What we can tell you about Gideon is that we are very excited. Why is Gideon doing the things he’s doing, and all of the questions the audience has, is exactly what we want them to be asking, and we’re going to be answering a lot of them in two particular flashbacks. One is Gideon’s; we’re going to see his entire life going from baby to 28 year old in one episode, and we’re going to see the Black Fairy’s origin story.

Source: http://www.ksitetv.com/once-upon-a-time/upon-time-eps-preview-midseason-premiere-beyond/143897/

Pretty certain that "his entire life going from baby to 28 year old in one episode" is 6x16 (Mother's Little Helper), and "the Black Fairy’s origin story" is, well, obviosuly 6x19.