Dark fairies surrounding a centaur on the Grip of the Shadow Plague cover.
A dark fairy is a fairy that was changed into a dark being. The one of the known occurrences was during the Shadow Plague at Fablehaven. It is stated that when the darkened fairy has been returned to its original state, the fairy will only remember their time of being dark if the fairy truly enjoyed being dark. When dark, all affected creatures appear to enjoy it. The other occurrence was when Ronodin took over The Fairy Realm.