Reduces damage from spells by half.
NulAll (バオル, Baoru? or バオール, Baōru?, lit. Barall), also known as Wall or Greater Barrier, is a recurring ability in the series. It is often a White Magic spell that protects against damage from all elements.
NulAll (WALL in the NES release) is a level 8 White Magic spell which grants Resist Fire, Resist Ice, Resist Thunder, Resist Earth, Resist Status, Resist Poison, Resist Time, and Resist Death. Unlike previous Nul spells, NulAll can only target a single ally.
Because of how the game is programmed this has the effect of nullifying the chances that elemental attack spells and enemy abilities will cause 2x damage rather than actually reducing elemental damage by half like in later games. Also, these status effects grant resistance to status inflicting spells and enemy abilities, as well as to all physical status attacks. With the exception of the spells Blind, Stun, and Kill, to which resistance provides complete immunity, the NES version always has a 1/201 chance of a critical success for any attacks/spells (based on D&D's critical success/failure rolls). In the case of status spells, this means that even resistant targets, including party members or the final boss, can still be hit with status ailments or instant death with a 1/201 chance. Later remakes appear to remove this, and resistance to an element grants immunity to status ailments caused by spells/abilities from that element.
It is important to note that having resistance to all elements does not provide any protection against spells or abilities that are considered to be non-elemental, such as Sleepra, Slowra and Trance, or in an unusual case, the instant death Mindflayers can inflict with their physical attack (which is meant to represent the character's brain being eaten). Only the target's natural Magic Defense helps to defend against non-elemental spells/abilities.
NulAll adds NulBlaze, NulFrost, NulShock, and NulTide. Kimahri's Mighty Guard Ronso Rage ability casts NulAll in addition to Protect and Shell. Sandy of the Magus Sisters is able to cast the spell. It is also provided by using the Tetra Elemental item.
Rikku can also mix several types of NulAll: the normal version affects one party member, Mega NulAll affects all party members, Hyper NulAll adds Cheer and Focus, and Ultra NulAll adds all stat boosts to the Nul-spells.
Greater Barrier is an enemy ability which grants Protect and Shell statuses and reduces damage by 1/3. It is used by the Shield Wyrm, the Lindwyrm, the Behemoth King, Belias, Zeromus, Ultima, Zodiark, the Bombshell, the Matriarch Bomb, Judge Ghis, Doctor Cid, and Vayne Novus.