Illusion is a discipline group regarding the branch of magic involving the creation of powerful and very vivid illusions, able to stimulate and thus fool the five natural senses.
Not much is given about this discipline though it is presumed that, similar Psychics, it mainly involves distorting the senses. It is suggested that Illusionists are able to conjure Illusions powerful enough to become corporeal, though this hasn't been expanded on as of yet.
The Illusionist Castle is located above The Sea but is invisible and only detectable by Illusionists. It is tethered to the field by a bannerless spiral staircase, which is also invisible. The staircase is a common center of amusement as students end up tumbling off of it after a night of partying at the Castle.
- Mirror Magic: The manipulation of mirror images.
- Invisibility: A major arcanum, as described by Quentin Coldwater. This involves scrubbing your image out of existence, and is said to take years to accomplish fully (though Illusionists are likely more adept at it).
- Camoflage/Cloaking: This involves taking elements of your environment (grass, leaves, stones) and glamoring them to mask your image. It is said to work best from a distance.
- Projections: An illusion executed around an area to make it look like another place.
- Sensory Manipulation
- Vanishing: This discipline was mentioned by Professor Sunderland while testing Quentin's discipline. 
"—cloaking, invisibility, and projections that will make the CIA look like amateurs. You’re a great liar, as is everyone in your Discipline. Have fun with that." - BrakebillsU