All this talk of the underword, besides me wanting to see hades because he would be hilarious. But what if emma is a parallel to Persephone? She is the savior and dark one. Persephone brings spring/summer (light)and fall/winter (dark) when she leaves
This is actually an interesting view. Myth states that Persephone when on ‘earth’ was this sweet girl who brought in the spring with her mother. If we look at her mythology in Hell she was a badass. While Hades is known as god of the Underworld she is known as Queen. She was stricter, almost merciless, than Hades and people didn’t dare speak her name.
If Persephone is brought in there could be a parallel or even a similarity to Emma. Savior Emma brings in hope and light when she is saving the town while Dark Swan bring in darkness and despair as she terrorizes it.
Like I said I could see similarities between the two.