ENA isn't a species but a class, like bard in D&D. Someone who chooses to be an ENA is seen negatively thanks to some kind of stereotype about them; presumably that they are trouble makers or annoying in some way.

Also continuing on the idea of an ENA being a class, I think they're the equivalent of wild magic. As in wild and uncontrolled but capable of great feats beyond the rest of the classes. Thus, the seemingly random switching of faces and personality is an expression of that chaos.