the anatomy is the main issue here, because as it is now, its just a yoshi head attached to a stickman body.

I'm pretty sure anatomy isn't quite as critical here as in some of the other entries.  Yoshi's anatomy is sort like a potato.  I think the anatomy's fine here.  The gun could use a revision.  The spark looks a little fire-crackery and not so much like a blast from a video-game-gun.  He could also shoot out a ball or a fruit like Yoshi does.  :)

Try learning to draw anatomy more fluidly. You need some basic skills.