Each creature in Niflheim is capable of having one very strong Fetish. If a lover satisfies this in Freya's Breeding Shop, good things can happen - or extremely wrong things depending on your own perspective and the Fetish at hand.
By satisfying the creature's listed Fetish requirements, you'll be awarded a bonus that could give nearly any type of breeding related benefit. Including previously LESP Item exclusive effects like Egg Copying and Gift Chance.
Creatures are not born with a Fetish, they must acquire it through breeding at least once.
Please be warned that you will not be told what Fetish your creature acquired when skipping the breeding sequence or when using your Breeding List, but rest assured that their perversions will develop either way.
The only way you can re-roll a creature's Breeding Fetish with a News Reporter Empusa's assistance.
In a Creature's Status Tab called "Breeding" you'll see its breeding Fetish, if it has one. This information will also be displayed when selecting it for breeding.
A Fetish can also be viewed while choosing a creature for breeding. You can view a complete list of all Breeding Fetishes at Information>Fetishes.