Ahh damn, I had a suggestion for you on how to make the marisa hats look a little better, but I didn't post it on your last image cause I don't like to criticize people. Now I can't remember what it was!!! :(
Find source and reference you want and draw them as much as you need. When you feel comfortable with your drawings start stylizing it in a manner you feel works with you. Play around with your art.
That or you could cel-shade more if the shape isn't the problem.
You want my advise? lol its exactly ThatOneGuy's advise! And not because he's one million times the artist I could ever hope to be, but because he is right. I have my yukkuri folder, and inside that I have my reference folder. Sorted by species I have reference drawing. You see I have trouble drawing so seeing how another artist visualizes and draws a specific thing helps me so much.
Since you seem to be a damn natural, a little bit of reference will probably go a long way! Listen, you've been drawing yukkuri for less than a month, its only natural that you will be unhappy with the way they look! Trust me a little when I tell you that you're doing phenomenally already, and that a little teensy tiny bit of practice may push you over the edge. You'll change from a good contributor to a great contributor in no time!