I love this.
The concept, the animation, the shading. It's all fantastic! For some reason this actually makes me think the song in my head.
The shading is awesome on this, especially on the yellow. The vibrant saturated colours really suit the expressions and bounciness of the emote. The expressions are great as well; they really tard the whole thing up, which I find awesome.
My only suggestion is that the animation of the hammer could be slightly improved. It looks a little odd when the hammer strikes down onto the yellow dude, lik there's no power involved. Try adding a few more frames to the 'back' swing of it, and hold one of the frames (the one before he strikes) for about 0.5-1 second and it should climax to a smoother beating.
Other than that, another fantastic work of yours. Your distinctive style is coming along nicely. :3