Null Magic (魔法無効, Mahou Mukou?), also known as Null-Magic and Magic Damper, is a status where the afflicted unit becomes completely immune to magical damage.
Null Magic is a status that makes Zack Fair immune to magic damage. It can be gained via the Digital Mind Wave by spontaneously rolling 3-3-3 outside of modulating phase, or via Cait Sith's Courage Boost ability.
Magical Masque makes the party immune to magical damage. It is learned on the Songstress dressphere for 20 AP, but the key item Magical Dances Vol II is needed to learn it. It is the reward for defeating the Experiment in Chapter 5 when all its stats are at level 5.
Yuna's special dressphere, Floral Fallal, has access to Barrier which nullifies magic damage done to the user. The Psychic dressphere has the ability Magic Guard which nullifies all magical damage done. It takes 80 AP to learn and Gravity Eater must be mastered.
The Magic Shield status prevents all magic from taking effect on the target, including status effect spells. Players may obtain the effect by using the items Spiritual Incense, Fool's Drink, Fool's Tonic, or Fool's Powder (the last of which also affects all players nearby, not just the user). Numerous monsters have special abilities that can gain Magic Shield, including the Ahriman family's Magic Barrier, the Hydra family's Polar Bulwark, the Magic Pot family's Spectral Barrier, the Ruszor family's Hydro Blast, and the Soulflayer family's Immortal Shield.
There is also a stronger form of Magic Shield that absorbs damage from magic as well as a weaker form that absorbs a fixed amount of damage before disappearing ala Stoneskin, but limited to magic only.
Magic Damper is a synthesis ability that negates all magical damage taken by the character, but makes them unable to be healed from damage or status with magic. It is obtained by equipping five items of the Ultimate Magic group. As only Snow and Fang have weapons in the Ultimate Magic synthesis group, they are the only characters that can obtain Magic Damper.