Illusion Casting is a power that a Caster has. It is the power to manipulate the appearance of an object, but not the actual object itself. Larkin once cast an illusion to make his eyes look like the green eyes of a Light Caster but they were really the eyes of a Dark Caster. He also cast an illusion to make his arms into snakes and make his eyes look like snake eyes. Larkin casts an illusion on the Lunae Libri so it doesn't get robbed.
In Dangerous Creatures, the doorman at Suffer casts an illusion to make a brick wall appear in front of Ridley when she got into Suffer and Floyd mentioned that he wouldn't be turned into Roger Waters and cast an illusion so that people think she was the lead singer of Pink Floyd.
Illusionists are often thought to be less strong or not as good as Shifters, but this may not always be the case. For instance, if a Shifter wanted to look dead, they would, if accidentally, commit suicide. But an Illusionist would be able to appear dead, thus tricking the minds of the other party. There is also a theory in which an Illusionist can fool with the mind's memories and create illusions in a person's mind.