I dunno if Ayla's the best example, a lot of her coming across female is because of the pose, floofy hair, and animal-fur bikini than anything particularly notable about the art itself.
Fair enough -- The pose definitely helps with that "feminine" look. But that actually validates the reason I said to study Ayla and used her as an example: There are way less pixels to work with in her case, and yet the artist managed to convey the "girl" look by offering more curves (by making her pose more "curvy") -- and since pixels dont do "curvy" very well (because, you know, they're square...), the artist used lighting and the pose itself to avoid the "boxy" nature of the pixels, lending to an overall "less-square" pose.
Sure, the anatomy of the original boss sprite there was definitely more manly, but the pose itself was too blocky as well. This emphasized the "square" nature of the male body over the "curvy" nature of the female one, which only emphasized the "male" appearance in the boss's anatomy.
That being said -- great job on the boss sprite edit, winged doom!
I like how you curved the hips more to align with the curvature of the legs in the animation. You overall made the "curvy" work. The addition of something going on in the breast area keeps the eye from assuming it is looking at a very muscular male torso -- especially when combined with the more curvy hips. It works great.
Regarding the smaller sprites -- I totally understand the trouble. It takes some "getting used to" when working that small.
The biggest thing to keep in mind on smaller sprites is that pixels can be "compressed" sometimes, which means you can use a pixel from another part of the palette to represent the "inbetween" state of the pixel as it is being "compressed" and then transition to the more prominent solid color. I don't see you doing much of this, nor do see too many colors you can use as an inbetween (for example, if you made the dress maroon, you could use the dress color to substitute for a darker overlapping shade that isn't quite as dark as the outline -- this is all assuming you want to keep the palette small of course.) This subpixel animation is almost mandatory for sprites as small as these, but for more simple sprites and animations with larger movements (such as moving the head and staff), this subpixel animation can be bypassed. However, in this particular case, you'll need some subpixel motion to make the character more believable if you want motion.
That being said, you can make the feet smaller and slimmer (and the hand holding the staff slimmer too) to emphasize she's still delicate underneath all the muscles. This can have the downside of making her come across as a transvestite. But if the bulky thing is intentional, this can't really be avoided.
On the other hand, if she is supposed to have a similar build as the boss (i.e. a bit more athletic), then you'll have to take a cue from Ayla above and use light and dark contrast along the length of her limbs to "pose" the thinner parts of her limbs in 3d space. This means you'll have to modify the "clear" direction of your light source to some extent in some areas where you need more contrast to represent the major planes of the body. The key point on this aspect is to try to represent "thinness" wherever you can.
Have you ever tried to render a gently-curving spider web or white hanging thread in pixels? -- This is a great practice for rendering "thin" stuff with "fat" pixels.
To be clear -- "infinite resolution" -- is what you're aiming for in this case.
In your mind, the thread should still be as thin as it really is, but as you place the pixels (and render the thinness), these pixels will follow where the super-thin thread would be in space, and in places where it curves, you gradually use a "subpixel" color that "compresses" the pixel with the nearest darker color to the degree in which that pixel has curved away from a straight line (which is the only time the basic "white" color of the thread is used, except in places where the curve needs that color to start curving back to another angle.)
This is definitely a skill that takes practice, but once you "get" the idea, it's pretty straightforward. You can string super "thin" pixels up like nobody's business. Being afraid of thinness with pixels is natural, but subpixels are your friend -- especially when you understand the concept of "infinite resolution" is just a fancy way of saying "use subpixels for rendering in places where it's necessary (i.e. where the pixels are "compressed" on the screen while rendering an object as if you, yourself, were the 3d GPU placing each pixel on the screen), and use regular pixels in places where it's not necessary for that kind of rendering."
I hope this makes enough sense to give you some direction on this process!
