In short, the main tank needs to hold aggro on any mobs not controlled by crowd control or an offtank. If the tank is holding multiple mobs it may be difficult to hold them all, so one or more may run towards a healer or overzealous dps. This occurs when the victim's threat exceeds that of the tank by a certain percentage (110% for melee and 130% for ranged.) For the tank to regain aggro, they must exceed the new target's threat by the same amount. There are a number of ways to do this. First, most tanking classes have some sort of taunt ability to force the mob back onto them, immediately increasing their threat to that of the person who currently has aggro. This will not hold the mob unless more threat is added onto it before the taunt duration ends. Secondly, the tank can simply use a few high threat abilities in a row to regain aggro. This is easiest done when the new target refrains from doing any action that continues to increase threat, such as damage or healing. Third, the new target can use a threat-reduction ability such as Feint or Fade, or a complete aggro-wiping ability such as Feign Death or Vanish. This will put the mob back onto the tank, provided the tank is directly below them on the threat meter. If a hunter is the target and feigns death, but the healer is directly below them, the mob will attack the healer and ignore the tank.
Tips for Helping the Tank Regain Aggro
- LET THE TANK KNOW. Most tanks will notice a mob has wandered off, others will not. If you are in a PUG, be safe and assume they won't. Type something! If you are on Ventrilo, tell them on there, making sure you use your character's name.
- DO NOT RUN AWAY. The tank can't regain aggro if you drag the mob away from them. Either sit still, or even better, run towards them.
- STOP ATTACKING THAT MOB. If you continue to build threat on the mob, it will become exponentially harder for the tank to grab it. If the cooldown on their taunt isn't up yet, you may be ensuring your own death. As a healer, pumping heals into yourself will ensure your survival, but make it harder for the tank to grab that mob. As the tank pays attention to it, other mobs may lose interest in the tank and go after the rest of the group or yourself, ensuring a wipe.