SPOILERS AHEAD! FOR ALL SEASONS OF ONCE UPON A TIME
First off, this video does a great job pin-pointing all the major dark moments in Emma's life. From her doubt in herself to her loses and the rejection of her power.
Once Upon A Time has been Emma's story from the first episode, and each trial brings her closer to the light. She has yet to deal with darkness.
Due to her circumstances, Emma has felt abandoned for most of her childhood, and it caused her to grow tough and guarded as an adult. As she walks the path of a hero, Emma learns that accepting her life and role as it is will only happen when she stops doubting herself. This is her first step down her own path of becoming a hero. The second step was to accept her past, and she used that knowledge to save her son from the darkness. The third step is learning what she can do. She must embrace her magic and accept it as a part of who she is. It took a long time for her to do this, and she still struggles with accepting herself as a hero, a mother and a magic user at times.
But this season will be her most difficult challenge of all: embracing her dark side. As she did sacrifice herself to the darkness, becoming the hero that she knew she could be, she still had issues with accepting her heart. This childlike part of Emma is always pushed away, and now, with darkness to tempt it, we will see this side of her character.
This is our first look at Emma, and already she seems a little childish, playing a cruel game of hide and seek. Her expression reminded me of Peter Pan when he is testing Hook. She acts on impulse as well, and before he can blink, the guard is dead. This is a scary moment to witness, because despite her act, Emma instantly regrets what she has done. You see it in her expression, as she stands there, staring at him.
There's another interesting detail in this scene: the diamonds.
Something to keep in mind here is that Emma did not become the Dark One to be evil. She did it to save Storybrooke, and the darkness seeped into her soul.
Each dark one has an element that is related to the soul tied to the darkness. For Rumple, it was gold. For Emma, it looks like it will be diamonds.
Diamonds are symbolic for healing, shining from within and they reflect light.
The word diamond relates to the word adamas, which means unbreakable or unalterable in Greek.
So the diamond is a specific symbol for Emma, in the fact that it disperses light.
Emma was made of light and love, and her soul is still in there, probably constantly battling the darkness. She is still aware of her actions, as we see in this clip, but she is surrounded by so much darkness, darkness that has been growing for centuries, that she is unsure how to stop herself.
It's already been confirmed by the writers that Emma will slowly turn dark, so this clip may be way later in the series, when it is more difficult for her to resist out of pure exhaustion.
I beleive that the child side of Emma, feeling abadoned and lost will become the shadow side that the darkness will attach to, but the diamonds are Emma's own strength, light within the darkness.
I hope this series reveals the reason Merlin believed that the only way to contain this horrible evil thing was to tether it to a human soul, because it seems to have a conscious of its own.
Because Emma is more light than dark, the darkness will eat at the light for a long time, but I think Dark Swan will be a projection of Emma's childhood self, the self she pushed away for a long time.
In Once Upon A Time true love does conquer all, but I'm not sure they will do a true love's kiss for this one. It didn't seem like that would work for Rumple, and it probably won't work for Emma.
It will probably be exactly what Emma said to her parents and to Killian that will at least reach out to her. They will have to find the light in the darkness to save Emma.
And now for Regina's role as saviour. This is an interesting story arc. We've seen Regina be a hero, but I imagine she still has demons to fight from her dark past. She may be Emma's only hope because she has been part of the darkness, and it nearly consumed her. (And she's not lying on the ground unconcious like Rumple)
I think the big moment in season 5, and the theme they have been going for since season 3 really, is the acceptance and love of the self. To love yourself as who you are. To accept your faults and weaknesses.
This was a similar motiff for Riku's story in Kingdom Hearts, and Lightning's story in Lightning Returns. Emma will probably have to accept her shadow side, and her parents, son and pirate will probably help her with that. It is the most difficult battle for any character to face, and it may be balanced through Regina's new role.
While Emma embraces the dark, Regina must embrace the light.
This is just a theory, but it comes from being a writer, a reader and an observer of characters.
The shadow is the scariest and most challenging villian for a character according to Carl S Jung. There are only two ways that stories have invented to defeat it: accepting it or banishing it.
This darkness was already banished by Merlin, so my theory is it will only be defeated once it is accepted.
That said, I'm both thrilled and wary of this season. It looks pretty dark.
An interesting twist would be Merlin needing to embrace his dark side, or his dark magic. I hope Morgana is involved because she is known to be his worst nemesis. Who knows, maybe she taught Maleficent how to be dark.
It will be interesting to see how they portray Emma's dark side, and how the characters will react.