RTF is a global modification that replaces all towns in the game.

Well, if it's for decoration, then bone dragons require too much mercury. And devils require sulfur.

I didn't say it was for decoration. I'm talking about the service, i.e., maintaining these creatures in the city. Moreover, the concept of "a lot" is vague. If ore arrives, say, in tons, then rare resources are mined in much smaller quantities (for example, 1 gram of gemstones may be valued as much as 2 tons of ore).