Mind Control

Mind Control is a shadow spell that allows a unit to temporarily take control of an enemy target for up to 30 seconds and use it to attack other enemies. In PvP, the duration is 8 seconds.

Functionality
Mind control serves as a unique form of crowd control in that not only is the target removed from the fight temporarily but the target's powers can be directed against other enemies. On a successful cast of Mind Control, the priest's viewpoint will shift to the controlled player or mob and the priest's movement keys will move this unit. The target unit's abilities will replace the priest's primary action bar and will be available for use. Mind Control forms a general-purpose crowd control similar to sapping and sheeping; however, unlike most other forms of crowd control, the priest himself is essentially removed from battle for the duration of the spell and cannot cast any of his own heals or attacks until the Mind Control is broken.

Mind Control's full duration is 30 seconds, but there are several factors which can cause it to break early. A break is checked vs mob's level / distance from controlling priest / resistances of target, every x seconds, and the spell can break without warning even if the channeling bar is still mostly full. In addition, if the MCed unit is moved too far from the controlling priest the spell will automatically be disrupted. Attacks directed against the controller will shorten the duration of the spell but will have no effect on the the target's ability to break free of their own volition. Death (of the priest or the MCed target), silences, and some other abilities will entirely disrupt the spell.

Casting Mind Control generates a great deal of threat from the controlled mob against the priest who controlled it. To this date it is not clear precisely how much threat Mind Control causes, but it is very substantial – a priest who releases a mob for it to be killed in an instance is well advised to do nothing else to generate threat until aggro has been rock-solidly established by a tanking character. The mobs will also tend to continue to focus on the priest for several seconds even through a taunt, so using Fade (after the taunt), Power Word: Shield, and/or Dispersion is strongly recommended. Apparently, mobs don't like having their free will stripped away by someone they can kill in two hits.

Elite mobs can generally be MCed, but not bosses. You can even MC other players, although you are limited to melee attacks while doing so. The signature usage of MC in PvP is to MC an enemy player atop a tower or other high place and then run that player off the edge, causing a large amount of falling damage (if not death) and removing them from the area.

See also a List of mind controllable mobs for information on MC-able enemies as well as their locations and special abilities.

Tips, Hints and Info about Mind Control

 * 1) Mind control duration is partly controlled by distance. The farther your 'pet' is from you, the higher the chance of breaking. Park it on top of yourself if you wish to reduce its chances of resisting - unless you have other plans in mind for it, OR if the NPC you are fighting has some sort of stun/cc (Shield bash/gouge/polymorph etc).
 * 2) Mind control a healer if it's available. Why spend your own mana and get possible aggro when you can easily mind control that medic and use its prayer of healing which heals for 30k+? Don't forget that the medic has 200k mana, meaning it can chain cast it for a while. And if it gets aggro and dies... just remember that it wasn't you.  Keep in mind, however, than many healer mobs have moderate cooldowns (5-30 seconds) on their heal abilities, so be cautious MCing even healer mobs if you are the sole healer for the group.
 * 3) Mobs within aggro range of an MCed target will regard it as hostile - they have no qualms over beating up a unit that was a trusted ally only moments before, so you can mind control something and let the surrounding 'linked' NPCs kill it. Note, however, that if the MCed target is freed from your control, they will once again regard it as a friend and will immediately seek another hostile target to attack - which may be you.
 * 4) Mind controlled NPCs have their own aggro; spells cast by an NPC do not get 'added' to your current aggro, so in group situations you do not have to worry about enemies that you attacked with an MCed mob favoring you over your tank.
 * 5) Mobs must take damage from players in order to generate loot; should they be killed solely by a Mind Controlled mob they will drop no items. In addition, a Mind Controlled mob will generate no loot if it dies while still MCed; it must be released if you wish to take its items.
 * 6) Mind Soothe is VERY useful in getting close to humanoid NPCs without them jumping you due to the 30 yard range of mind control. If you want them to focus on pet and not on you first (Remember aggro rules) use Mind Soothe.
 * 7) Effects that reduce an enemy's shadow resistance (such as the Warlock's Curse of the Elements spell) can decrease a mob's ability to resist or break free of Mind Control.
 * 8) Priests should attempt to use high mana non-damage spells like buffs or heals to burn the mob's mana away before it is released to be killed.  If it has an aura or shapeshift, if should also be turned off before releasing it, forcing the mob to recast it when released (or preventing it if sufficiently mana starved.)  Cooldowns should also be burned just before releasing.