Mechanic

A mechanic is a way in which your game character interacts with the rest of the game world. Most of the time the game's normal mechanic is in effect, but there are debuffs that can change your mechanic. Debuffs that impose mechanic-altering effects come in all dispel types, and some have no dispel type at all, meaning that they either must run their course and expire over time or have a specific way in which they can be removed.

For example, if a Priest or Warlock puts a Fear mechanic on you, there are two options available to you: if you have the "Insignia of the Alliance/Horde" trinket and are a Druid, Mage, Paladin, Priest, Rogue, or Warlock, or if you are Undead (see Will of the Forsaken), you can remove the Fear effect yourself. Or, if there happens to be a friendly Priest or Paladin (or Warlock with a Felhunter) around, they can remove the effect as well, as both [Fear] and [Psychic Scream] cause Magic debuffs.

If one attains the second PvP rank (Corporal/Grunt) in the Honor System, one can purchase an "Insignia of the Alliance/Horde" trinket, which when activated can remove three class-dependent types of mechanics; this power has a cooldown of 5 minutes. This table shows which class's "Insignia of the Alliance/Horde" trinket removes which effects. A "Y" means the class's trinket can remove the listed type of effect, while an "N" means it can't.

Class	Charm	Fear	Polymorph	Root	Snare	Stun
Druid	Y	Y	N	N	N	Y
Hunter	N	N	N	Y	Y	Y
Mage	N	Y	Y	N	Y	N
Paladin	N	Y	Y	N	N	Y
Priest	N	Y	Y	N	N	Y
Rogue	Y	Y	Y	N	N	N
Shaman	N	N	N	Y	Y	Y
Warlock	Y	Y	Y	N	N	N
Warrior	N	N	N	Y	Y	Y

Charm

(Examples: [Seduction])

You can't control your character, who stands still, usually with hearts floating above his/her head. Some classes' PvP trinkets cancel this effect, as does the Undead racial ability Will of the Forsaken.

Confuse

(Examples: [Polymorph], [Scatter Shot])

You can't control your character, who wanders aimlessly. There may be items that help remove this effect (if this happens as part of a Polymorph, see Polymorph for more), and these would of course be usable in this situation.

Damage Reduction

(Examples: [Curse of Weakness], [Hex of Weakness], [Touch of Weakness])

The damage dealt by every melee attack you make is reduced. There is to my knowledge no way to remove this mechanic specifically, although the debuff that causes it is usually either a Curse or a Magic-type debuff, which can be removed in the usual way.

Daze

You move slowly. This is a lot like the Snare mechanic, although it has the added effect of knocking you off your mount, if you're on one to begin with. These effects are usually very short-duration.

Fear

(Examples: [Fear], [Howl of Terror], [Psychic Scream])

You run uncontrollably away, out to a certain radius, then mill about randomly, also uncontrollably. PvP trinkets for many classes remove this effect, as does Will of the Forsaken.

Periodic Damage

(Examples: [Corruption], [Rend])

You continue to take damage every few seconds for the duration of the effect. The amount of damage depends on the effect, as does how often the damage occurs. There are items (such as the mighty  [Luffa]) that remove physical Periodic Damage mechanics, which are known as Bleed effects.

Polymorph

(Examples: [Polymorph] (duh!))

This is basically a combination of a Confuse effect and a Transform effect. The reason why it's a separate mechanic from those other two is that there are items (for example, the PvP trinkets) and class abilities (such as the Druid ability to shapeshift) that remove both components of a Polymorph effect.

Possession

(Examples: [Mind Control])

You are under the control of a mob or another player.

Root

(Examples: [Entangling Roots], [Frost Nova])

You are frozen in place, attached to the ground. The Gnome racial ability Escape Artist can remove most Root effects.

Silence

(Examples: [Counterspell])

You are unable to cast spells. This may be from a Magic-type debuff, in which case a Priest or Shaman ally could remove it from you, although you couldn't do so yourself.

Sleep

(Examples: [Hibernate])

You are asleep. Your character stands still, head bowed, with "Zzz" above his/her head. Very similar to Stun; you cannot move or take any actions.

Snare

(Examples: [Curse of Exhaustion], Frost Bolt)

You move more slowly than normal. Escape Artist can remove some Snare effects.

Stun

(Examples: [Gouge], [Hammer of Justice], [Kidney Shot], [Mangle], [Pounce], [Sap], War Stomp)

You are unable to move, cast spells, or use items, with the exception of those which allow you to break free of stun effects, of course. Some of the PvP trinkets will remove this.

Transform

(Examples: Druid shapeshifting, [Polymorph])

You look like something else. When imposed upon you by another, this is usually combined with a Confuse mechanic, but not necessarily -- several items and effects in the game will transform you, but the only confusion they cause is in the minds of onlookers.