A Twilight Foulfeather is a Fallen in Oninaki.
Fowl Fallen with insect-like wings. Foulfeathers attack by firing magic from their barrel-shaped beak. They can shoot these powerful projectiles in three different directions at once.
Encyclopedia of Fallen 1-2
It is said the leaflike patterns on Foulfeather wings are veins that allow the Fallen to absorb atmospheric magic. The wings of each species are patterned differently as a result of the various habitats in which they live.