Board Thread:Spoilers!/@comment-2153169-20150419225421

'''The series has a nice habit of teasing the next big bad. Will that be the case here, too?''' "Yes, absolutely. It’s a big reveal. The new big baddie is going to be really bad. It’s the unimaginable. It’s the worst thing that could possibly happen. It’s going to be tough for everybody. It’s going to be distressing for fans."

source: http://spinoff.comicbookresources.com/2015/04/19/once-upon-a-times-prince-charming-crosses-the-good-to-evil-line-teases-new-big-bad/

Now, I'm thinking it is gonna be Dark Emma aka Black Swan; and you? :) 