Nul-Spell is a recurring status effect ability that makes a person immune to a specific type of damage, usually elemental.
NulBlaze, NulShock, and NulFrost make their first appearance as White Magic spells in the original game reducing incoming elemental damage, along with NulDeath and NulAll.
NulBlaze, NulShock, and NulFrost appear as White Magic spells along with NulTide. The four Nul-Spells are located in Yuna's section of the Sphere Grid. NulAll can be accessed by Sandy of the Magus Sisters and be generated via Rikku's Mix Overdrive, along with its variants: Mega NulAll, Hyper NulAll, and Ultra NulAll.