Not so much "supernatural" as... something that defies the world's natural order. Strange, alien creatures, their mindsets often impossible to understand. And always dangerous to some degree.

[He gives her a sidelong glance, assessing her reaction. Does she still apply "aberration" to herself after that clarification? Perhaps in all technicality, yes, but he cannot quite place her on the level of Illithid after their conversations thus far.]

Think of awful, awful things. In this case, I'm talking about a creature called a mind flayer. Capable of great psionic power, with wet, rubbery flesh, elongated head, and a flourish of-

[He raises his hand, puts it close to his mouth, and wiggles his fingers. Tentacles.]

-writhing tentacles for a mouth.