I love the circular comp! Don't know anything about the holidays and mythology that you mentioned but the piece looks interesting anyway.
And the creature is awesome. I think you wanted the banshee to be the main focal point, but I would add a bit more light to the creature, at least to its focal area. And some cast shadows, like from the creature's legs to the cocoon.
Also, the left foot bugs me because the toes are too symmetric and the left leg gesture is almost a straight line. My eyes just keep returning to this foot and staring at it. Btw nice texture on those legs!
Another thing is that the spider net looks too digital compared to all the rest. Have you tried using pencil tool presets in PS or some pencil brushes?
The banshee's right foot looks fine, but I just wonder what foot anatomy you had in mind. Raptors and birds usually have an additional finger behind, for balance, so from this angle it would probably be seen like here
.
Although, as your banshee is fictional and probably even does not walk much but mostly rides the creature, maybe she doesn't really need that hind finger.