Did you use the entire sprite as a bounding box and/or use pixel detection on the entire sprite? If so, I strongly suggest not doing so in the future. The boss being above the player character becomes unintuitive and annoying as a result of the hitbox covering more area than the context would imply.
Other than that, it's a pleasing little game. The dog was cute too. I personally think the boss had too much health, but my experience with other popular games seems to indicate that I get bored of bosses to quickly.