Board Thread:General Discussion/@comment-8345449-20140513141958/@comment-9232373-20140513161810

So many possibilities. We don't even know for a fact Marian died the first time, just that Robin thought she did. She may have gone on to be an important influence in the history of the EF, and now with her in the future, many things could change. Or she did die the first time, but wasn't supposed to, and "fate" was what helped allow Zelena to do her time portal, to pull her out so she is still alive. Fate is never known until the end.

My theory, Marian attacks Regina and Robin has to kill Marian to save her.