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.