>>41239392some say that Gardevoir are herbivores but I don't know of any other creature with such a developed brain that isn't an omnivore.
My headcanon is that they eat primarily plants but supplement it with energy they suck from living creatures that enter their territory. They don't hurt them, just make a lot of creatures a little more tired. If they're really hungry they might hit a creature with Hypnosis and Dream Eater them,
It seems like a Fairy kind of thing to do.