Please don't save your pixel art as a .jpg. It messes up the look and makes it a pain to edit if that happens to be your only copy.

I think this piece could benefit from the removal of (at least inner) outlines, particularly.

Also, you might want to address the form and design mistakes before you move on to tuning-up the animation, as it could just get messed up again when you fix those things.

Hehe, nice bell curve we've got going here. I personally fit into the lower end of said curve.

Heh. Demoscene.

I suggest you darken the outlines somewhat on the third samus to find a middle ground between it and the first. The middle samus's border has 1px lines simply stacked on top of each other; it will never look good to use that technique. Try using a style that more or less antialiases the light blue to the black over a longer distance than conventional.

Thanatos looks like he could benefit from more highlights and a less harsh style of shading. Also, consider adding just a tad of color to your greys, plain grey isn't very interesting.

The parrot is very nice, but the one to the right is lacking contrast on the green, and some darkness variation of the inner lines would make tham more suited to the size. I really like the middle one now.

The bat doesn't really have much to crit, though the animation looks technically well-executed. One suggestion, though, is to bump it up to an even 4 colors and antialias the eyes, though that might not fit well with the style. Maybe post a side-by-side comparison?

I think you did overdo the aa on the practice. You might want to use that much if you're doing a glow, as in the samus, but for a normal object it's just too much.

For stars/space, I think this piece needs to be much darker overall. Try decreasing your saturation while you're at it. Also, the hue shifting is nice, but very strong. I would make it more subtle.

You have a nice start on the sword-bear thing, but once again the hueshifting is too strong and it could use a tone between the blue and the black. Also, the eyes aren't compliant with the style you have everywhere else, being sharp and not really as smooth as other things. One last thing is that you might want to use some different palettes or subpalettes to differentiate objects.

The butterfly-thing is nice, and I like the feather texture on the wingtips, but it does seem to lack clarity of features; I'm just guessing at your intentions here. I'm not sure exactly how to correct this, but that's why it's a public forum. XD

These are absolutely great for first pixels, though that isn't to say that they're perfect. The sword weilder's sword is much too long and generally the wrong size. That image could also do with some selout to break up the shoe, arm, and pant outlines.

The rabbit is a nice piece of work, though I think the eyes could stand out a lot more and some inner aa on the ears would break up the jagginess there.

The art is generally good, but a few small things stick out at me. The mountains in #1 and the trees in #3 have a thin dark outline and that would probably work better with the style if it was a thicker shadow. Also, the bottom-left status bar in screenshot #5 looks rather jaggedy due to the pixels in vertical lines there.