Board Thread:Spoilers!/@comment-5899967-20150208192922/@comment-24674051-20150327135202

I think that both Merrin and Victoria are done with taping for OUaT as of "SFtDV". Since Merrin is appearing after getting her happy ending, it is likely just flashbacks (though they could pull her into present day again, depending on the story requirements). So I think that episode 4x18 probably ends the Queens of Darkness arc, and Merrin and Victoria will be off set (at least for this season, if they manage to keep Cruella alive as well, then who knows what future seasons hold).

4x19 through the Finale is probably a combination of Lily, Maleficent, Snow and David's dirty deed, potentially Dark Emma, and Operation Mongoose, which I am getting the feeling are very much intertwined, and compose a conclusion to this years action with the Author, and set up the next season, probably with some sort of major cliffhanger.