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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 . 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.
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 each other.  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 ( is a partial exception). As well, many boss monsters can stack several copies of the same DoT on the same player.
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 or the Dwarven racial ability . Also, Paladins can dispel nearly any debuff on themselves by using , as can Mages by using .
- Weakened Armor
- Effect: -12% armor
- Physical Vulnerability
- Effect: +4% physical damage taken
- Death Knight: (Frost)
- Death Knight: (Unholy)
- Hunter: (Pet) Boar:
- Hunter: (Pet) Ravager:
- Hunter: (Beast Mastery): (Pet) Rhino:
- Hunter: (Beast Mastery): (Pet) Worm:
- Paladin: (Retribution)
- Warrior: (Arms, Fury)
- Magic Vulnerability
- Effect: +8% spell damage taken
- Weakened Blows
- Effect: -10% physical damage done.
- Death Knight: (Blood)
- Druid: (Feral, Guardian) Thrash
- Hunter: (Pet) Bear:
- Hunter: (Pet) Carrion Bird:
- Monk: (Brewmaster)
- Paladin: (Protection, Retribution)
- Slow Casting
- Effect: -30% casting speed
- Death Knight:
- Hunter: (Pet) Sporebat:
- Hunter: (Pet) Fox:
- Hunter: (Pet) Goat:
- Hunter: (Beast Mastery): (Pet) Core Hound:
- Mage: (Arcane):
- Mortal Wounds
- Effect: -25% healing received
- Hunter: (Beast Mastery): (Pet) Devilsaur:
- Monk: (Windwalker)
- Warrior: (Arms)
- Warrior: (Fury)
- Patch 3.0.2 (2008-10-14): There is no longer a limit on the amount of Debuffs a target can have on them at any time.
- Patch 2.0.1 (2006-12-05): Debuff slot limit increased to 40.
- Patch 1.7.0 (2005-09-22): The debuff limit has been increased to 16 (from 8). In addition, the client will now display all 16 debuffs.
- ^ Blizzard. Spells & Abilities. Retrieved on 2009-06-12. “A debuff is a buff with negative effects, such as Curse of Tongues. Spells like these do damage over time, or modify your character in a negative way.”
- ^ Daelo 2008-12-03. The Debuff Limit and You. Archived from the original on 2008-12-03. Retrieved on 2009-06-12.
- ^ Vaneras 2006-08-14. 14/08 New debuff limit. Retrieved on 2009-06-12.
- ^ Zarhym 2008-08-28. 3.0.2 - On Debuffs, Buffs, and Raid Stacking. Archived from the original on 2008-08-28. Retrieved on 2009-06-12.