I suppose any world might have them. How could we even tell, until they decide to show their power...?

[For a moment he wonders if some of the locals secretly have the powers of a Ditto, but he squashes that thought quickly.]

Certain powerful monsters and Eidolons have the power to take a human form, though it can be seen through by those who are attuned to power and magic. However, it is not a common ability.