Yo!
Here are the things I believe you must work on.
1. The head, he shouldn't headbang that much, try only moving it 1 or 2 pixels in a horizontal range.
2. He's waving his arms a bit too much, aswell as the cape. Since he's running(?) he should have a more fierce movement than plain walking, but you should move his arms inwards a bit and make the cape smaller. The collar of the cape doesn't have to move that much either I believe.
3. His feet. Hmm... Well I guess they are too big, maybe make him show less "skin". Let the cape cover it. But don't make the cape larger!
4. You forgot to draw the golden border on his cloth in 2 frames. I think it would look better if you used it all the way.
5. About the colors, I tend to like to use to many myself, but It all depends on what platform the sprites are intended for. You could try to limit your pallette before drawing, seeing as you used green, red, violet, gold and black, maybe you could get away with one of each color plus one lighter & darker version of it to shade.
6. I also think you should lower the FPS from 12 to 9 to make his movement smoother.
7. You might already use one, but references are great! I'm guessing you were influenced by this?
as you can see, one way would be to let your little guys head be still, while having his pigtail pendle.
I hope you don't mind, I tried to edit it a little.

I also changed the colordepth to 16 (4bpp).
Looking at it now I believe the collar and the cape still needs to be fixed. Also you could try removing the hands completly (cover them with the cape). Try some random stuff and see how it looks.
I hope somone else can take over from here.

And about the Imp, it' looks cool- just add eyes! Prefferably bright yellow, red or white. That would make it look more evil

Good luck to you.