A gigantic serpent-like B.O.W. (Bio-Organic Weapon), able to freely move in and around buildings by destroying the walls.
It secretes a fluid that can diffract light when it is excited by sensing prey, allowing it to blend into its environment, similar to how optic camouflage works. Although it loses this ability when severely wounded, its skin hardens considerably instead. Its name derives from the Serbian for "Illusion".