When Magic Booster is used in the 2013 PC re-release, the player's inventory gains 100 Zombie spells, among other basic spells.
Zombie is often drawn from undead enemies. The player can also get one Zombie spell from Zell's "love quest" if they give Hot dogs & Pink as the answers to a "survey" held by girls at the library, and later return for the results. However, different answers yield superior spells as reward.
Zombie will inflict the Zombie status effect on a target that is not immune to it. This makes the target undead, causing them to receive damage from curative items and magic, as well as instantly kill them with reviving abilities such as Life and Phoenix Down. It also causes the targets to gain innate immunity to Instant Death and Doom, take double damage from Holy-elemental attacks, and halve physical damage. Draining HP from a Zombie unit damages the drainer, unless both the caster and the target are undead/Zombie. The status effect lasts until the status is removed, and persist after battle.
Zombie can be cast using the Magic command, Selphie's Slot Limit Break, or Rinoa's Angel Wing if she has it in her inventory. Casting Zombie in battle increases compatibility with Doomtrain by 1, but lowers compatibility with Carbuncle by 0.2.
Zombie can be junctioned to ST-Atk-J to inflict Zombie on enemies with a physical attack, though this is a niche use for the spell. A more common use is to junction the spell to ST-Def-J to resist against Zombie, as 100 Zombies can lead to immunity to Zombie. This can be important against many enemies that can inflict Zombie, as it can be a very harmful status effect. Its ability to halve physical damage can be situationally useful, however, as it stacks with Protect, such as against Omega Weapon's Terra Break, although the player will then need to heal via elemental spells with elemental absorption in place via junctions.
The Zombie spell can be useful against the Sorceress enemies during the gauntlet against them later into the game, as they are not immune to it and can then be easily dispatch with curatives.