Good art principles in place here. Pixel tech needs attention. You're on the right track!
I love this piece!
Keeping a low colour is necessary because in pixel art it is extremely important to put each pixel by hand - so the fewer colours the less work to do! Even so, I was surprised by the need for low colour when I started, but the more I did it, the more fun it became!
As for reducing the colour count, try putting the URL of your piece into this wonderful web utility, by our very own Hatch, and it'll be very easy to see which colours are almost identical to each other, and can be removed.
Once again, though, I can't tell you how much I love every part of this!
For your second piece this is pretty damn good. My second piece sucked almost as bad as my first. =D
Also agreed about dithering the powerbar, not needed. There are plenty of extra reds from the hero's hair, you could even use some of the purples from the background. There are a number of unnecessary jaggies that don't make logical sense but otherwiseI really like this.
(the gradient on the word boss makes it hard to read and doesn't actually do much for it. I think just a flat gold would look a lot better. )
You could make the hero stand out more. Otherwise great stuff.
Yes, i am totally new with pixel art, it's my second. And you're right, i ll try to work with less colors for the next. :) (that ll be hard!!)
I can tell you're a good artist, but if you're serious about "pixelart" you should really try to work with less colors and palette management. This is just a 256 color, possibly color reduced, 24-bit palette...quite a no-no in my book. Mockups usally have an increased acceptance for high colorcounts...but with images like this it's a pure gamble if you get rejected or not. I'd love to see you try doing something with a limited palette, I'm sure you could do it.
And why dither the powerbar when you have all those colors?
Beautiful work! I like it!