Elementals are fine as long as they are relatively rare and more like animals than humans. Thanks for the idea, I will update the core rules to reflect the fact that the world should be mostly like the real middle ages, i.e. we don't want fantasy creatures on every corner. However, some creatures being common in some places is fine with me, so if there is one area where people have earth elementals as workers - that's ok. The basic standard is that it should be unusual enough that visitors would mention it.
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