is the running sprite your reference / is that the only pic of him?
I think yours looks more like a teen in a penguin cotume, and the little one looks more like a tuxedoed man with a mullet. The pants look like sweatpants, are they supposed to be?

but anyway, the first thing I suggest you do is increase the contrast between the colors, I can barely see the face.

And then, look at pictures (aka references) to figure out how to draw things more realistically, I suggest working on the face and pants. Just collect some pictures that you want to use, and make comparisons between yours and the pictures.

Then try to make yours look more like the pictures, don't be afraid to be messy, blob around a bit, you don't need to pixel right now, just work on shadows and highlights. Then you can clean it up after.'


And the background is pretty blank, but gradient backgrounds are very hard to do in pixel art. Usually they're disguised by clouds or something like that. Of course you can dither, but it's hard to pull off, but if that's what you want to do, look around at how some other people dither, learn a few methods and you'll be good.