Taunt Mechanics Guide/Discussion
Taunt is an ability shared by all Tank classes in some form. Taunt has 3 main functions:
1. Forces the mob to attack you for a set duration of time (3 seconds base).
2. Sets your threat equal to the current aggro holder (I.E. at 100%)
3. Makes you the current aggro holder.
There is a small difference between #1 and #3 in that #1 is called a Fixate. It just makes you the current aggro holder for the duration of the debuff. A few of the tank classes have other abilities that do #1, but do not do #2 or #3. Mocking Blow, Challenging Shout, and Challenging Roar are among these Fixate only abilities. Those abilities that only have the Fixate property usually Fixate for longer (6 seconds rather than 3). The difference for #3 is that it makes you the current aggro holder until someone pulls aggro or you lose aggro through some other fight mechanic (or death). It doesn't have a time limit or debuff associated with it.
NOTE: There are various combinations of these 3 things that can occur on special mobs. Some mobs are totally immune to taunt and none of the 3 occur (this also can happen through diminishing returns). Some mobs will take the fixate but not affect your threat or aggro status at all. The Instructor Razuveous adds are among these. In general, though, taunts will either fully work, or fully fail.
Taunt - Spell - World of Warcraft -- Single Target 30 yard Taunt
Growl - Spell - World of Warcraft -- Single Target 30 yard Taunt
Righteous Defense - Spell - World of Warcraft -- 3 Random Targets 40 yard Taunt (all targets must be targetting the same player)
Hand of Reckoning - Spell - World of Warcraft -- Single Target 30 yard Taunt
Dark Command - Spell - World of Warcraft -- Single Target 30 yard Taunt
Death Grip - Spell - World of Warcraft -- Single Target 30 yard Taunt with Pull Mechanic
Challenging Shout - Spell - World of Warcraft -- AoE 10 yard Fixate
Challenging Roar - Spell - World of Warcraft -- AoE 10 yard Fixate
UPDATE: In patch 3.3, Blizzard turned off Diminishing returns for most mobs.
For enemies that have taunt diminishing returns enabled, this is how DR works: if you taunt every time on cooldown, then the first taunt works as normal, the second taunt will work as normal, but only fixate for 65% the duration (1.95 seconds), the third taunt will work as normal, but only fixate for 65% of the second taunt's duration (1.2675 seconds), and so on. The sixth taunt will go immune and none of the effects of taunt will apply.
# Taunt Diminishing Returns: We've revised the system for diminishing returns on Taunt so that creatures do not become immune to Taunt until after 5 Taunts have landed. The duration of the Taunt effect will be reduced by 35% instead of 50% for each taunt landed. In addition, most creatures in the world will not be affected by Taunt diminishing returns at all. Creatures will only have Taunt diminishing returns if they have been specifically flagged for that behavior based on the design of a given encounter.
Diminishing returns will reset if you do not taunt for a set period of time. As of this time the duration of the diminishing returns seems to be around 18 seconds. I tested this by taunting on cooldown over and over again and noting the times (UPDATE: I tested this during the 3-taunt era, but the results should be the same, just after 5 taunts instead). The first three taunts landed, the next two were immune, and the next one landed. Testing also shows that immune attempts don't start the diminishing returns timer as the sixth attempt landed. As a note, Fixate only abilities like Challenging Roar also apply diminishing returns to targets and will count against your taunts in that respect.
As of a Cataclysm patch, taunts no longer miss. There are no "hit mechanics" for taunts now.