Quality of the lining could mean like blending the colors together, so it doesn't have that "stop on a dime feeling" if that makes any sense lol. Assuming thats what Thefarmer100 meant of course. Or he/she could mean that it looks too pixelated and the lines could be smoothed out a little more on these designs (of course if pixelated was your intention then it looks great! Its like it could fit right into one of the Gameboy games!).
I do agree with the background color suggestion though, black doesn't look appealing for some pixelated designs.. I actually did notice it technically had no background because I could see the Newgrounds background. In my opinion you should add a bright enough background to see their outlines, It looks more appealing to the eye to be able to see it rather than it fading into the back.
Besides these small things^ I love your idea of Pokemon evolution dresses, The Arbok one is my favorite which is why i choose to review on this one!
Love it
5/5 - Idea
4/5 - My personal eye appeal
Hope my review helps!