Debuff, also known as Enfeebling or status ailment, is term referring to a negative status effect in Final Fantasy series. A positive status effect is called a "buff". In Final Fantasy XIII and Final Fantasy XIII-2, debuffs are the effects that reduce enemy stats; other negative effects are are split off into the Debilitation category.
Although the concept of debuff appears in all Final Fantasy video games, the following titles use the term explicitly. For a full list, see status effect.
XI Debuff is a term for spells and effects that grant status ailments or lower enemy ability scores or attributes. Generally these can be spells like Blind, which lowers enemy accuracy, or Gravity, or lowers enemy evasion, rather than spells like Fire which is a direct damage spell or Poison or Foe Requiem which is simply damage over time. In Final Fantasy XI, magic like this is found mostly in the category of Enfeebling Magic.
XIII Debuffing status ailments are those which hinders target's stats. Status ailments which are classified as "debuff" are Debrave, Deprotect, Defaith, Deshell, Imperil, Poison, and Dispel. Chance of inflicting debuff-classified status ailments can be raised with Improved Debuffing and Improved Debuffing II passive abilities which can be gained by equipping Vanille with Belladonna Wand, its tier 2 version, Malboro Wand, or its final tier of Nirvana.
XIII-2 Deprotect, Deshell, Imperil, Poison, and Dispel return as debuff-classified status ailments. Debrave and Defaith are only available as the Feral Link of Tezcatlipoca. Improved Debuffing and Improved Debuffing II are red-locked passive abilities which are not available for infusion. Improved Debuffing is an ability of Bamapama, Black Chocobo, Hedge Frog and Mimi. Improved Debuffing II is an ability of Chelicerata, Forked Cat, Garuda and Necrosis.
The distinction of debilitation status remains, but availability is curtailed. Curse, Fog and Pain can only be used by tamed monters; Slow can only be cast by the Feral Links of Don Tonberry, Nekton and Samovira; Daze is not available. Improved Debilitation is a red-locked ability of Illuyankas. Improved Debilitation II is also red-locked, and held by Ahriman and Silver Lobo.
This game refers to persistent status effects like poison, blindness, and petrification as debuffs in online Help. Within a Record dungeon, debuffs may persist between battles or until the player party retreats from the dungeon to the hall in which that dungeon resides. Most effects can be removed in Camp using Mythril or purchased Gems.