Spark's Sprites

[SparkMouse]

I'd say No Face looks quite a bit better in the whole contrast department and the same goes for Kiki's balance issues. Her CSS sprite is still a tad wonky though. Her cheek buldges a little too much. Here's a little list of somethings I think might help:

1: Smooth her chin.
2: Center her mouth.
3: Lower her nose.

I also think you should center No Face's CSS sprite a little more. It would give it a more uniform feel in comparison to the rest.

Hopefully that's better.

The problem with No-Face now is that he has a ridiculous colour count. Try to keep it to about 16 colours or so. I'd also work on one sprite at a time. Kiki's anatomy is a little bit off, for example. Her legs are too short, and her head is too far back on her neck. Here are a few pointers for human anatomy:
1) In general, the length of the leg is approximately the same as the height of the chest and the head
2) The head connects to the neck at the back, leaving space for a chin.
3) The arms, when straight, should reach approximately half way down the upper leg.
4) The width of the hips should be approximately equal to the width of the shoulders.
5) The hand, when splayed, should just cover the face.

A lot of those you've done fine with, but I'll draw your attention to numbers 1 and 2.

Anatomy is the part you should pay more attention to, because if you don't study it enough, the results will not be favorable. Acknowledging the proportions, such as leg length, hand size, etc. will improve the quality of the sprite.

Kiki's hair is kinda spiky at the bangs, but try representing it as groups of hair instead of trying to reproduce every spike. Trying to do so results in a far messier hair.

Pixelart is also about ignoring small enough details and keeping the important elements to make a character recognizable even in a small resolution.

I redid the legs starting from extending the original skeleton to be as long as the chest and head combined, as you said, then refilling it in the same steps as the rest of the sprite. They're a few pixels longer now, and I'm unsure of whether or not to detail her knees in or if they're just barely covered by her dress.
I also edited the head slightly, moving it one pixel to the right to accommodate your suggestion for the neck (@Hoeloe), and also smoothed her hair out toward the bottom (@Gors), however I kept the bangs as they were.

About No Face, I need a good way to show gradual transparency for his body. The reason there are so many colors is because I used a gradient in Photoshop for the newer version; if you have a way to do it with just a few shades, I'd appreciate it.