Advice on my Rejected Sheet?

[striker212]

I've recently made a custom sprite sheet for a Super Mario World Goomba. The first time I submitted it, it got rejected for being "not up to quality standards". I thought it was because the icon had a white background rather than a transparent one, so I changed the icon and tried again. However, my sheet was rejected once again for the same reason. Can any of you help me pass the standards and get my sheet accepted?