I am trying to achive my grass to look like this

Try to get those colors first, then draw with them (he has 4 colors, you have 2 - no wonder it's hard to reproduce). Also your tiles are faaaaaar to small to emulate this sort of grass: This grass lives from single, large clouds of darker leaves, while single tiles like yours can only create small-environment repetition.

Also look at the shape of these clouds and how they grow.

If you ask me, just paint the grass of that scene on a big canvas until it looks right; Then you can try to make it smaller (by drawing it again). You should learn how this grass feels, the spirit of this grass, then you can take up that spirit and draw it on a somewhat smaller canvas. But if you go too small (like you possibly must), no chance. It's just not the right grass for that.

EDIT: this post only refers to the first variant. I didn't see the update when I posted this.

:O http://www.youtube.com/watch?v=86MY-quTiJs

There is one thing I can comment on though: There are some pixels on the outline of the snake that seem strange... One example would be at the lowest part of the snake, where you antialias and there is this dent...
And out of curiosity, why do you antialias the snake? The skull looks awesome without antialias.

EDIT: You should stick with the first variant. (even though the outline of the snake is better in the third variant).

Walk cycle for a janitor robot (hence the hat!)



As it is, it looks a bit.. chunky/pixelly. I can't really AA because there will be different colored backgrounds. C&C would be appreciated  

I have few comments on the art, it is quite good. He seemed a little bit to wiggly for me (like he'd be made from jelly), but you have hanged that. The cap still seems to move too much (both the cap itself which seems to grow and shrink and the thing above his eyes which is really wiggly).

However, I'm wondering why he's a janitor and why that thing chases him. Judging from the mockup he wasn't a very good janitor.
Mario the plumber at least had those pipes that he could go through, but in general there was no reason for mario to be a plumber (except for his clothing which was a consequence of the pixel & color restrictions).
You do not have such restrictions so you better have a good reason for him to be a janitor, for a janitor to be chased by such a terrific monster, and for a janitor to run through such shabby corridors.

Haha reminds me of the Diablo intro.
The legs of the raven look like they are on the same plane. Are you sure you need two pixel outlines on the raven?
On the left horn of the skull, there is a curve of light pixels at the lower left side that I don't understand. Neither do I understand the black directly above it. I guess that is because the raven is lightened from top left, while the skull is lighted from the left. And even then there's some light missing to the left of the horn.
I'm only going to mention the many dents in the horn because you're probably work on these anyway.
One more thing I do not understand: Do the horns point towards the viewer or towards the background? The legs of the raven seem to make no sense.

The skull looks great but the right eye (the bright one) deserves some attention. There are two occurrences of parallel jagged lines: white/black at the otside and lighy grey/white at the inside, to left part of the eye each. I believe you should work on these regions. And then I'm not sure whether I agree to the shading of the inner of that eye... To me it looks like there's a pillow-shaded sphere in there popping out of the eyeshell (?).
Other than that, great jaw, great raven, great nosething, great horns.

PS: I believe the snake is too much. Can't be such a cruel world if it's so full of animals that two different kinds gather at one random skull.

EDIT: The longer I look at it, the more it seems that the main problem are the legs of the raven. Make the raven sit on the horn correctly and it will already improve by a huge shot. Then shade the legs correctly and we'll see how that works out. (plus the other things I mentioned beside the shading).