I personally think the amount of enemy statues in the game is too low. They are also way too hard to find. I suggest you allow crafting of the statues at a Heavy Work Bench and Ecto Mist. The recipe could maybe be something like 50 stone + a banner. This would also allow you to have enemy statues for late game mobs because if you could find the underground early game you could trigger them and the mob would kill all of yout NPC's.