FFS, man your Newgrounds link is invisible while actually shooting, but if you click where it is it takes you to the front page anyway. Good GOD that is annoying.
Also, you should make it so that you can shoot all around you instead of just in 4 directions. Or at the least, have some degree of auto aim. It gets very frustrating trying to shoot things and only juuuuust missing by a pixel.
Other than that, some varying music would be nice, as well as some different sounds for the different types of mushrooms. Not horrible overall, but could be polished a ton more.