Illusion is an effect type. Illusion powers decieves the mind or the senses. Illusions often obstruct vision or redirect attacks. If an illusion power deals damage, the damage itself is not an llusion. Users or arcane magic, such as wizards, consider illusion to be one of the schools of magic. [RC:118]
A creature immune to illusion is not affected by the nondamaging effect of a illusion power.[RC:225]