Debuff

A debuff is the contrary of a buff. It is an effect that while it persists hampers the target in some way. Among other effects, debuffs frequently lower attributes, hinder the effectiveness of the target's actions, or cause damage over time.

Sometimes the term debuff is also used to describe the act of removing buffs on hostile targets, but it is better to refer to such an action as a dispel or cure after the common spells that remove such effects. Another popular name for removing debuffs is decurse.

A good example for a multi-function debuff is the Hunter's Mark. All attackers on that target gain increased ranged attack power; additionally the target cannot hide from the Hunter, no matter if they stealth, turn invisible, or morph into beast form. Hunter's Mark, being in the Arcane school, is removable with Cloak of Shadows and other skills and talents which remove magical debuffs.

Debuffs come in many varieties and most of them are race/class specific spells or abilities.

Debuffs are also color coded, with poison debuffs having a green border, magic debuffs a blue border, physical debuffs a red border, diseases a brown border, and curses a purple border.

Limitations
There is no effective limit on the number of debuffs that may be applied to a creature at one time. Prior to the release of the Wrath of the Lich King expansion, a single target could have at most 40 debuffs at one time.

Similar debuffs generally do not stack with eachother. One prominent exception is damage over time debuffs (DoTs): multiple copies of the same DoT will generally stack when applied by different players, and when applied by the same player to different targets (Living Bomb is a partial exception). As well, many boss monsters can stack several copies of the same DoT on the same player.

Examples of Debuffs

 * Warlock: Curse of the Elements
 * Hunter: Scorpid Sting
 * Druids: Faerie Fire
 * Warrior: Demoralizing Shout
 * Rogue: Wound Poison
 * Priest: Misery

Dispelling Debuffs
A list of types of debuffs, the classes that can remove them and the earliest level that class gains the ability.
 * Poison: Druid, Paladin
 * Disease: Paladin, Priest
 * Magic: Priest (has both a single-target and AOE version), Restoration Druid (talented), Holy Paladin (talented), Restoration Shaman (talented),
 * Curse: Druid, Mage, Shaman

Examples of Abilities that Cure or Dispel

 * Druid: Remove Corruption
 * Mage: Remove Curse
 * Paladin: Cleanse
 * Priest: Dispel Magic, Cure Disease, Mass Dispel
 * Shaman: Cleanse Spirit

Unclassified Debuffs
Some debuffs are not classified in any way, and as such can not be dispelled by any class. There are some exceptions to this - some Bleed effects, which are unclassified, can be cured by using a Luffa or the Dwarven racial ability Stoneform. Also, Paladins can dispel nearly any debuff on themselves by using Divine Shield, as can Mages by using Ice Block.

List of shared (non-stacking) debuffs

 * Armor reduction
 * Sustainable
 * Faerie Fire / Faerie Fire (Feral): -4% per application, stacks up to 3 times, also prevents stealth.
 * Tear Armor: Raptor ability, -4% per application, stacks up to 3 times.
 * Corrosive Spit: Serpent ability, -4% per application, stacks up to 3 times.
 * Expose Armor: -12%.
 * Sunder Armor: -4% per application, stacks up to 3 times.
 * Unsustainable
 * Shattering Throw: -20% for 10 seconds with a 5 minute cooldown. Stacks with sustainable debuffs.


 * Attack speed lowering (melee)
 * Frost Fever: Caused by Icy Touch, Hungering Cold, glyphed Howling Blast and glyphed Scourge Strike. Can also be caused by using Pestilence on a nearby creature that already has Frost Fever. Increases melee and ranged attack intervals by 20%.
 * Infected Wounds: Tier 8 Feral Combat talent, 3 ranks, causes Mangle, Maul and Shred to apply the Infected Wound debuff, which increases melee attack interval by 20% @ max rank, also reduces movement speed.
 * Judgements of the Just: Tier 9 Protection talent, 2 ranks, causes Judgements to increase melee attack intervals 20% @ max rank.
 * Earth Shock: Reduces melee and ranged attack intervals by 10%, 20% when talented.
 * Thunder Clap: Reduces melee and ranged attack intervals by 10%, 20% when talented.


 * Attack speed lowering (ranged)
 * Frost Fever: Caused by Icy Touch, Hungering Cold, glyphed Howling Blast and glyphed Scourge Strike. Can also be caused by using Pestilence on a nearby creature that already has Frost Fever. Increases casting time and melee and ranged attack intervals by 14% (20% fully talented with Improved Icy Touch, a tier 1 Frost talent with 3 ranks).
 * Slow: Tier 7 Arcane talent ability, increases melee and ranged attack intervals by 60%, also increases casting time.
 * Earth Shock: Reduces melee and ranged attack intervals by 10%, 20% when talented.
 * Thunder Clap: Increases melee and ranged attack intervals by 10%, 20% when talented.


 * Attack power reduction (melee and ranged)
 * Vindication: Scales with level, -574 fully talented @ level 80.


 * Attack power reduction (melee only)
 * Demoralizing Roar: -408 @ max rank (~571.2 fully talented with Feral Aggression, a tier 1 Feral Combat talent with 5 ranks), Bear Form and Dire Bear form only.
 * Demoralizing Screech: Carrion Bird ability, -410 @ max rank.
 * Curse of Weakness: -478 @ max rank (573 fully talented w/ Improved Curse of Weakness, a tier 2 Affliction talent with 2 ranks), also reduces armor.
 * Demoralizing Shout: -410 @ max rank (-574 fully talented with Improved Demoralizing Shout, a tier 2 Fury talent with 5 ranks).


 * Casting time increase
 * Slow: Tier 7 Arcane talent ability, +30%, also increases ranged attack intervals, each mage can only have one Slow spell active at a time.
 * Mind-Numbing Poison: +30%, each weapon can only have one poison applied to it at a time.
 * Curse of Tongues: +30% @ max rank, each warlock can only have one active curse per target.


 * Critical strike chance against target increase
 * Master Poisoner: Tier 9 Assassination talent, 3 ranks, +1/2/3% against targets poisoned by the rogue.


 * Critical strike chance against target increase (spells only)
 * Improved Scorch: Tier 4 fire talent, 3 ranks, gives Scorch a 100% chance to apply the Improved Scorch debuff @ max rank, increasing spell critical strike chance by 5%.


 * Damage received increase (bleed)
 * Mangle (Bear) / Mangle (Cat): Tier 9 Feral Combat talent abilities, +30%.
 * Stampede: Rhino ability, +25%, 12 second duration, 1 minute cooldown. Rhinos can only be tamed with Beast Mastery, the tier 11 Beast Mastery talent.


 * Damage received increase (magic)
 * Ebon Plaguebringer: Tier 9 Unholy talent, 3 ranks, requires 3 ranks of Crypt Fever. The death knight's diseases cause Ebon Plague instead of Crypt Fever, in addition to Crypt Fever's disease damage increase, Ebon Plague increases magic damage by 13% @ max rank.
 * Earth and Moon: Tier 10 Balance talent, 3 ranks. Causes the druid's Starfire and Wrath spells to apply the Earth and Moon debuff, which increases magic damage taken by 13% @ max rank.
 * Curse of the Elements: +13% @ max rank, also reduces Arcane, Fire, Frost, Nature and Shadow resistance.


 * Damage received increase (physical)
 * Savage Combat: Tier 9 Combat talent, 2 ranks, causes the rogue's poison debuffs to increase physical damage caused to the target by 4%.
 * Blood Frenzy: Tier 9 Arms talent, 2 ranks, causes Deep Wounds and Rend to increase physical damage caused to the target by 4%.


 * Healing received decrease
 * Permafrost: Tier 2 Frost talent, 3 ranks, -20% @ max rank.
 * Aimed Shot: Tier 3 Marksmanship talent ability, -50%.
 * Improved Mind Blast: Tier 3 Shadow talent, 5 ranks, -20%, 100% chance of being applied @ max rank by Mind Blast while in Shadowform @ max rank.
 * Wound Poison: -50%, each weapon can only have one poison applied to it at a time.
 * Furious Attacks: Tier 8 Fury talent, 2 ranks, gives whit melee attacks a chance to reduce healing by 25%, stacks 2 times, higher proc rate @ rank 2.
 * Mortal Strike: Tier 7 Arms talent ability, -50%.


 * Hit chance decrease (melee and ranged)
 * Insect Swarm: Tier 5 Balance talent ability, -3%.


 * Hit chance against target increase (spell)
 * Misery: Tier 8 Shadow talent, 3 ranks, causes Mind Flay, Shadow Word: Pain and Vampiric Touch spells to increase spell hit chance against the target by 3% @ max rank.