I rely love this. Although I think you could work on the anation of the stairs by having it expand horizontally as it gets hit, thus conserving its mass! And I think you could make it get compressed by three pixels, rather than one! I also love the particle effects that fly out when the stairs get hit!
I love the movement in the body! The experssion is the cherry on top 
You are totally right, it would improve a lot by expanding horizontally! I will try it, thanks!