Illusion is a powerful being within Oolbatism. While not worshiped by the Batsi, who have no official gods, its power and role within the religion is similar to that of an evil deity. Its primary objective seems to be to take control of mankind and the world for unknowable purposes. As a being that exists outside of reality, Illusion is never referred to using gendered language.
Batsi believe that mankind was created to inhabit the True World, but that Illusion trapped humans in a lesser realm under its control, which includes Khadaka. Why, or for that matter how, Illusion did so is a matter of significant dispute that the Oolbat has never felt need to clarify.
In this role, Illusion is believed to be in some amount of opposition to the Creator and in direct conflict with the Oolbat and the Batsi. It seeks to prevent people from reaching the True World, but is held at bay by the force and will of the Oolbat and their sacred artifacts. As such, Illusion is only directly observed acting during the Age of the Seeker. Outside of this time, it has a host of subjects that serve it, many of them incorporeal. Other traditions of Khadaka associate these servants with the Wandering.
Illusion is an amorphous being who exists beyond human perception and understanding. As such, no two attempts to describe it match.
Sylanthal believes that Illusion is another name for the Nameless One, known in Phaelism as Ngv. As such, those within the order who spend time in Frindar actively support the Oolbat and denounce Illusion. There have been attempts to be present and offer aid to the Seeker upon the death of an Oolbat, in the hopes of directly confronting Ngv, but none have yet managed to be in Kendrin at the right time. There is speculation that this is a purposeful hindrance, though no one knows who is behind it.