I love this concept! Aside from how it suits the theme the idea of a plump dragon squashing greedy intruders from its treasure is really cool and funny. The art also sells the idea really well with the dragon's expressions and animations and so does the music and sound! The blend of 2D and 3D is really well done and I love the glow on the coins and the death particles.
I feel like the delay between the fall and the "draggable state", though necessary, is a tad too long though and having it shortened would improve the experience exponentially as it would contribute to the flow of the game and help with the fact that you can't see enemies spawn from the side if the dragon sits there(which is usually the case as you can't hold it in the air for long).
The direction of the coin fall when you hit the enemies that pick them up, I feel should point towards the treasure as they're as good as gone when they're picked up by the robbers because they fly out of the screen even when you manage to squash them.
Otherwise this is really cool!