Power Word: Shield
Priests rely on various Power Word spells, a couple of buffs and a pair of attacks that will be commonly seen used by priests of all specs. The most common and probably most important one among these is Power Word: Shield, which is a damage mitigation spell that will keep a priest or her allies alive. Priests rely on a lot of self-buffs, so it's pretty important to get them off when you engage. Offensive dispels such as Purge and Dispel Magic or even Spellsteal are great spells to use against priests. Warriors can go for Shield Slam and hunters can use Tranqulizing Shot. Classes without offensive dispels must rely on consuming the shield with damage instead. The spell has a short, four-second cooldown but the good news is that it also applies a debuff called Weakened Soul, preventing the application of another Power Word: Shield for another 15 seconds. The 4-piece PvP set bonus will reduce that to 13 seconds, so try to keep track of the debuff whenever you can. Your best opportunity to deal damage is when Power Word: Shield is off and Weakened Soul is in effect.
Power Word: Fortitude and other self buffs
Priests also have an important buff that increases their health, which means removing it is almost like landing an attack. Power Word: Fortitude can also be improved through talents, and almost every priest who PvPs will have the improved version. It's important to keep the priest stripped of all buffs such as this one and Divine Spirit and Shadow Protection because it becomes easier to target the more important shield buff. In PvP, even the most seemingly worthless buffs function as a buffer to protect other, more important spells. Power Word: Fortitude has no cooldown but is a pretty expensive spell for a priest to keep recasting and priests would sooner heal themselves. Priests also use Inner Fire, which helps them against melee classes. The good news is that fast attack classes such as rogues can dispel this rather easily by consuming its charges and not too many priests will reapply it mid-combat as there are far better spells to spend a global cooldown on.
Is it worth dispelling? On it's own, probably not. (Riedelin correctly noted that Inner Fire is no longer dispellable) But it's absolutely critical to keep a priest's buffs to a minimum.
Shadow Word: Pain and other offensive spells
This is the third standard spell that any priest will use. Shadow Word: Pain is instant cast, allowing priests to keep moving throughout the battle. Most healing priests won't bother with anything else offensively, especially when they're focused on survival. Also expect them to throw out the more utilitarian Devouring Plague, which also heals them. Keep in mind that Shadow Word: Pain is a magic effect and Devouring Plague is a disease effect, so being able to remove one or the other will help ease the pressure on you defensively. Despite the fact that a priest will probably be healing on the battlefield, you'll always have to watch out for a Shadow Word: Death as a gambit, too. A priest that has created some distance and has time to cast can also cast Mind Blast, but don't worry too much about it. Unless they're seasoned PvP veterans, most healers will have tunnel vision regarding their roles and won't access their offensive repertoire the way a shadow priest would.
This is one of the best peeling spells in the game, and all priests know how to use it mostly because it's one of those spells that serve them well while leveling. Psychic Scream is also the priest's most clutch and powerful crowd control ability (although the audacious will use Mind Control) for PvP. Most priests will use it to scatter melee and to peel at the first opportunity to start the cooldown, which is at 30 seconds. This makes it easier to track and worthwhile to use a cc-break on. This is arguably a PvP priest's favorite spell and they will use it often so watch for it. It's a Fear effect, so be aware of the spells that allow you to break or prevent it such as a Tremor Totem or even another priest's Fear Ward.
Dispel Magic and Mass Dispel
As powerful as priests are when it comes to buffing themselves, they also have the best magical dispels in the game. Dispel Magic and Mass Dispel are both offensive and defensive dispels, allowing priests to remove buffs from enemies and debuffs from their allies and themselves. The best priests use these abilities judiciously, enabling themselves freedom from magical snares and roots and removing pesky buffs -- Mass Dispel is one of only two abilities that counters a Paladin's Divine Shield. PvP priests -- shadow priests, in particular -- also sometimes use Glyph of Dispel Magic, making their dispel a heal as well.
Priests are a fearsome opponent for any spellcaster because of Mana Burn. Although not as powerful as it once was, Mana Burn timed and spammed right can quickly deplete your mana pool. The most basic tip to avoid it? Line-of-sight. This is harder to do in the Battlegrounds than in the smaller, controlled spaces of Arenas, but is still a good thing to remember for casters. It is from the shadow school, so interrupting or locking out this spell probably isn't the wisest thing. Out of all a priest's spells, you should be more concerned about the spells they can draw from the holy school, namely...
Needless to say, every priest knows how to heal herself. Renew is likely to be the most commonly used, as it has excellent synergy with Power Word: Shield. It is instant cast, affording priests great mobility, and is a heal-over-time spell on top of a priest's numerous self-buffs. By now it should be obvious that a priest is at a disadvantage against classes that have offensive dispels and interrupts (congratulations, Shamans). Managing to keep a priest stripped leaves them with little alternative but to go for heals with a casting time such as Flash Heal or, more rarely, Binding Heal or Greater Heal. If you can interrupt spells, wait for those as they'll lock out the priest from over half of her spells and most healers won't be familiar with their spells from the shadow school except for Psychic Scream.
Because of their extremely high survivability, it will be common to find discipline priests in PvP and the comparatively squishier holy priests less frequently. The two specs have different tools and play differently from each other despite both being dedicated to healing (one could also argue that discipline is more about mitigation rather than healing). Of course, shadow has its own unique play style and wonderful toys, as well. Tomorrow, we'll take a look at the three different specs to give you an idea of what to expect when they PvP and what you can do to counter them.
Zach delivers your weekly dose of Battlegrounds and world PvP in one crazy column. Read about how to defeat your most feared opponents, beginning with Death Knights, Druids, Hunters, and Paladins. If you don't learn anything, at least find out more about who whupped your butt.