Almost all MMOs use this aggression mechanism, some call it hate, others aggro.
By default all mobs have an “aggro table”. A set of numbers that determine which player it is going to show love and affection towards.
The only thing that can change a mobs mind is mobility. Death is of course the most straightforward way to deter a mob from chasing you. Other than that a mob that is pinned by longshot will attack those in melee range that has the highest aggro, and ignore those it was chasing. You can continue to increase your aggro while ranged but he will only continue the chase after the loss of mobility wears off.
Being slowed does not change the aggro behavior, hence a slowed mob will continue to chase a tank if he is still top on the aggro table.
Every mob starts with zero aggro. It resets when there is no one left on the table (running out of range), and ends an encounter. The mobs returns to its position.
For example :
All mobs have aggro range, that is affected by the level of the player entering it. Think of it as personal space vs how attractive (or how rich) the person approaching you is.
Once triggered, range aggro only happens ONCE per encounter. Therefore, anyone else walking into the aggro range while the encounter is happening will have no aggro.
Aggro is generated this way :
1) Proximity aggro. Only happen to the first person to get it.
2) Any damage inflicted on the mob generates aggro.
3) Any buffs or heals to people who are on the aggro table.
4) Taunts. Warcry , pollen ring and bolas are high aggro generating abilities.
A druid casting breath on a group will generate aggro accumulated across ALL who are healed.
Generally the tank or DPs will have more aggro than the healer, except when new adds are called by the mob.
The adds being called immediately gains 1 point of aggro for anyone that is already on the callers table. A healer will naturally be on the top of this new table, them being vegans and all.
Now tank aggro only scales with vitality and melee combat. Vitality being the main stat and melee combat affects both the scaling as well as if the taunt will even land at all. Missed taunts does nothing except make big hulking tanks weep.
Stacking on melee combat gear is only viable thru hotswapping, and if the tank is well geared. If your clan is not gearing the tank well enough, you only have your own greedy selves to blame. (Yes this is a self serving statement, as shameless as it may be. Tanks are made to be thick no?)
There is not enough points for a tank to max all survival skills and both taunt skills, so to min max we use gears to offset this handicap, as well as raise skill levels to 50, above the 45 soft cap.
This is by far one of the best tanking charm out there, it shaves 15 skill points. It costs an arm, a leg, a newborn and a lifetime supply of hot crispy bacon. Some tanks also wear skill rings to max ALL the important survival and aggro skills.
A tank without aggro, is simply a weak DPS holding a fanciful shield and dashed druidic hopes.
Is there anything else you want to know about aggro?