As an idea to fit the theme and restriction, this is really good. I'm working for the dungeon boss, and throwing stuff over the edge. Generally, I really like the concept of defending a castle by chucking stuff off it.
The gameplay needs some tweaking. I think there are two main problems. First, it needs more feedback for my actions. Second, my decisions need to mean something. It doesn't seem to matter what I choose to throw over the side, other than armour, which is always useless because all the minions die before it spawns.
The art is great, if a little mismatched.