Hi Chip, solid concept! Though I'm confused about the two arms coming out from the sides. The main flow of the drawing appears to be from the center branching out, so the arms conflict with that to me. Are the arms Maleficent's hands? It appears they are two right arms so I'm not sure. Perhaps the amulet and poison apple could be graphical elements on their own, like part of a background pattern?
I agree the Last Princess should sort of appear on the poster, but it could be subtle...maybe a tiny light-colored silhouette facing down Ursula?