World of Warcraft™

Last update: April 16th 2012, patch 4.3.2

Hello everyone, and welcome to Lux et Umbra. This is a guide for Priest-related game mechanics. It is intended to be a guide to how stuff works while also functioning as a handbook of compiled factual information and numbers for all priests, new and old, pve and pvp, healing and shadow. If you're wondering about the thread title, "Lux et Umbra" is a Latin phase meaning "Light and Shadow." I hope the information contained here is helpful to everyone, as I have a lot of fun rewriting it and adding things as the game changes.

Special thanks to Nightshroud for writing the original version of this thread, Constie for his update of the original thread as well as his assistance in updating it once more, Dusknoir for fact checking, Whitetooth for compiling information about spell resistance, Kieble-Eredar for the nifty haste calculator, and everyone with a beta key who provided the community with numbers/formulas since I myself did not have access to the beta.

Table of Contents

I. Stats
II. Stat ratings, Mastery bonuses, spellpower coefficient, and haste tables
III. Miscellaneous mechanics, spell, talent, glyph, mastery bonus, and gem notes

I. Stats:

Spell power and Intellect

Spellpower and Intellect increase the effect of your damage and healing spells by an amount determined by what's referred to here as the spellpower coefficient of each spell. For example, the coefficient of Heal is 36.2%; If you have 5000 spellpower, Heal will heal for 5000 * 0.362 = 1810 more than it would at 0 spellpower. Intellect is associated with red gems (Each stat mentioned in this guide is associated with a primary color and also its hybrid color variants which for red would be orange and purple). See section II for a list of spellpower coefficients. Intellect, in addition to increasing spell power, will also increase your mana pool, spell critical chance, and the amount of regeneration granted by spirit.

Mana regeneration

There are several different sources of mana regeneration:

Mana per 5 seconds, which is directly increased by Spirit. Spirit is associated with blue gems. Intellect (Red gems) also increases the amount of regeneration that Spirit provides. Base regeneration is 5% of a player's base mana (This applies to all classes), which for a level 85 priest is ~1029.

At level 85, Spirit regen works off the following formula: 0.016725 * spirit * sqrt(intellect)

With Discipline or Holy Masteries, you gain 50% of spirit based mana regeneration during combat. Holy priests can spec into Holy Concentration, bringing their spirit based mana regeneration in combat up to 80%. For combat regen, the formulas are:

No Holy Concentration: BaseRegen + (SpiritRegen * 0.5)
Holy Concentration: BaseRegen + (SpiritRegen * 0.8)

Let's say I'm a holy priest. I have 1029 base regen as mentioned above, 8100 Intellect and 2500 spirit. First I figure out my spirit based regeneration using those numbers, then I cut that down to 80% and add that to the base regen.

Mastery

Mastery is a new stat introduced with Cataclysm and is associated with yellow gems. For every x mastery rating you have, you gain 1 mastery. All players start out with 8 mastery. At level 85, 179.28 mastery rating grants 1 additional Mastery. Mastery increases one of the bonuses associated with speccing into your primary tree, such as Shadow Orbs for shadow priests. For every 1 mastery you have, one of your mastery benefits for each spec will begin to increase. Per mastery point, Shield Discipline's (Discipline) effect increases by an additional 2.5%, Echo of Light's (Holy) effect is increased by an additional 1.25%, and Shadow Orb's (Shadow) effect is increased by an additional 1.5%. Be careful when you look at your spec's mastery tooltip. It displays a rounded number, but the game uses more precise values in its calculations.

Base mana

Spells don't actually have fixed mana cost numbers, but rather cost a certain percentage of your base mana, which is a number determined by class and level and nothing else. For level 85 Priests, base mana is 20590.

Section I Continued

Spell hit

Non-healing spells have a base chance to both miss their targets and be resisted by them. The miss chance can be removed via the spell hit stat, which is increased by certain talents, hit rating on gear, as well as gems. Hit rating is associated blue gems. A target's spell resistance can be ignored by gaining Spell Penetration (More on this below). The base chance to hit varies with your target's level relative to your own as well as whether your target is a mob or a player, like so:

Target level    PvE     PvP
±0                     96%   96%
+1                     95%   95%
+2                     94%   94%
+3                     83%   87%

Raid bosses are level +3, meaning you need a total of 17% spell hit to always hit. Spell hit also reduces the chance for spells such as Mind Control and Shackle Undead to break early. When you hover over your spell hit chance in your equipment screen, it will tell you your miss chance against mobs of your level and anywhere from 1-3 levels higher than you. Hit caps are covered in Section II.

Spell Criticals and Critical Strike Chance
Most spells and abilities that deal damage or healing have a chance to cause critical strikes, dealing 50% additional damage or 100% more healing to their target. Priests have a baseline critical strike modifier of 50% for damaging spells and 100% for healing spells. Shadow Priests get a passive called Shadow Power for choosing that specialization, bringing their critical strike modifier for damaging spells to 100%. At level 85, 178.28 critical strike rating or 648.91 intellect is equivalent to an additional 1% critical strike chance.

Spell resistance and penetration

Resistance cap for level 85 mobs: 1763
Resistance cap for level 88 mobs: 2172

Spell Penetration is obtained through PvP gear, enchants, and gems (Spell penetration is associated with blue gems). If a target has 130 shadow resistance and you have 80 spell penetration, your spells treat them as if they have 130-80=50 shadow resistance.

For those interested in mechanics details, two separate rolls are involved when a spell is cast at a target and both rolls again for any periodic checks (Also referred to as "Heartbeat Resists").

<Hit roll>
The first roll is based on relative level between caster and target. Casting at a higher level target is much more likely to miss than casting at a lower level target. The attacking caster can stack Hit to reduce her chance of missing the initial cast or experiencing an early break. Resistance stats on the defender do not counter the attacker's Hit stat. See the section on Hit stat right above this one.

<Resistance roll>
The second roll is based on the attacker's level versus the target's adjusted resistance stat for that school of magic. The maximum effect of resistance gear is to reduce incoming damage by an average of 75%. This caps out at 1763 resistance for level 85 (Players) and 2172 for level 88 (Raid bosses). There are some formulas involved in the calculation of average damage reduction among other things. Average damage reduction appears to follow this formula:

AveragePercentResisted = AdjustedResist / (AdjustedResist + ResistanceConstant)
Where AdjustedResist = TargetResist - SpellPenetration
The formula for the resistance constant, which is also the value at which you get an average 50% damage reduction, can vary with your level:
Level 1-20: 50
Level 20-60: 50 + (AttackerLevel - 20) * 2.5
Level 61+: 150 + (AttackerLevel - 60) * (AttackerLevel - 67.5)

The constant for a level 85 attacker would be 587.5 (Following the 61+ formula) and the constant for a level 88 raid boss would be 724.

So for a level 88 raid boss casting a spell at a player with 500 resistance...

(500) / (500 + 724)
(500) / (1224)
AveragePercentResisted = 40.85%. This percentage would also be displayed in your ingame character sheet under your Resistances.

Average percent can be anything from 0% to 75%. Most spells are 'binary': they either fully fail or fully hit, average is frequency of failure. Other spells are 'direct damage' and can partially resist at multiples of 10%. Resistance is still useful in any amount because the probability of each 10% multiple adjusts for every point.

Dual elemental damage such as Frostfire or Shadowfrost checks against the lower of the two resistances on its target to determine resists. If your target has 200 Shadow Resistance and only 50 Frost Resistance, Shadowfrost damage treats it as if it has only 50 resistance.

Sidenote: There's no such thing as Holy Resistance. Higher level mobs do have a school-agnostic resist mechanic which can't be countered by Spell Penetration (This still applies with dual elemental damage).