Lux et Umbra - A Priest Mechanics Guide

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Last update: November 16th, 2015, Patch 6.2.2
Note: I am Nysem of Mal'Ganis now.

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, and everyone else that isn't mentioned here but did something that they feel contributed!

Table of Contents

I. Stats and Stat ratings
II. Spell, talent, glyph, and racial notes

I. Stats:

General Overview

This section outlines stats that are useful to priests, what they offer, and how they work. Priests will find Stamina, Intellect, Spirit, Critical Strike Rating, Haste Rating, Mastery Rating, Multistrike, Leech, Versatility, and Avoidance to be useful.

In WoD, stats are categorized into three types:
- Primary stats are those such as Intellect, Strength, etc (Intellect is the only primary stat you want).
- Secondary stats include Crit, Haste, Mastery, Multistrike, Spirit, and Versatility.
- In WoD, there is a new category called minor (aka tertiary) stats which includes Leech, Speed, Avoidance, and Indestructible. These stats may randomly appear on PvE gear drops, meaning some "Swords of 1000 Truths" will have them and others will not.

Spell power and Intellect

Intellect is converted into Spell power at a 1:1 ratio. Spell power will then increase the effect of your damage and healing spells by an amount determined by what's referred to here as the spell power coefficient of each spell. For example, the coefficient of Smite is 92.44%; If you have 4000 spell power, then Smite will deal (4000 * 0.9244) = 3697.6 damage. In WoD, most spells have had their base values removed so that the damage/healing (before buffs/passives) is determined only by their spell power coefficient. Some spells do appear to still have base values, so there may be more on that later.

Spirit and Mana Regeneration

Passive mana regeneration, or Mana per 5 seconds, is where priests receive a significant portion of their mana regeneration. All players have a base rate of mana regeneration, but that amount is directly increased by Spirit. The formula is 2% mana per 5 seconds baseline + 4.12207024 mp5 for every point of spirit. Holy and Discipline Priests find this useful as it becomes more difficult to run out of mana and allows the use of expensive spells more often. Shadow Priests do not have a use for spirit.

For Holy and Discipline Priests, the Spirit based portion of your regeneration is reduced to 50% when in combat. The formula for mana regeneration in combat then becomes 2% mp5 baseline + 2.06103512 for every point of spirit (notice the spirit portion is cut in half). Shadow Priests do not have any spirit based regeneration in combat, they will only regenerate the base 2% mp5.

Despite having no spirit based regeneration, Shadow Priests are not concerned about mana when performing their rotation - damage spells cost microscopic amounts of mana and your base mana regeneration will regenerate much faster than you can possibly spend it doing damage. So what function does mana serve for Shadow, then? Currently its purpose is to limit the use of certain spells such as Flash Heal and Mass Dispel without adversely affecting your ability to deal damage.

Fun Fact: Given the rate of mana regeneration, it is possible to convert other effects, like trinkets, that regenerate mana into mp5 (any value of mana per time is fine as long as you use the same units) to make easier comparisons when making gear choices. Power Word: Solace is an easy example. Under ideal conditions you may use it 6 times per minute, for 12% mana per minute, which is 1% mp5, which at level 100 means 1600 mp5 (1% of a 160k mana pool). 1600 mp5 divided by the value of a point of spirit in combat (2.06103512 mp5) comes out to Power Word: Solace being equivalent to 776.3 spirit when used optimally.

Mastery

Mastery is a stat granting an effect depending on your specialization. For every x mastery rating you have, you gain an additional percentage of your spec's mastery bonus (The value of x depends on what spec you are as well). As you gain more mastery, the Mastery effect that you learned becomes more effective, such as a Holy Priest's Echo of Light. The tooltip displays a rounded number, so if you gain 1 mastery rating and the tooltip doesn't change, that point of mastery is still working.

Mana pools and mana costs

Spells don't actually have fixed mana cost numbers, but rather cost a certain percentage of your mana pool. Both mana cost and mana pools are numbers determined by class (Spec for some classes), level and nothing else.

Talents or effects that passively reduce mana costs apply to the base mana costs of spells, and stack additively; The mana cost reduction from Power Infusion stacks multiplicatively with others because it's an active effect as opposed to a passive one. However all the passives have been pruned out of the game, so there is that.
Section I Continued

Spell hit

In the past, spells had a chance to miss their targets and you could reduce this chance through Hit Rating. Hit Rating is no longer in the game, so you will not have issues hitting your target anymore. Although you will no longer worry about this as a stat on gear and your hit chance is generally always 100%, missing is still a thing that can occur in the game. You may run into some kind of debuff that reduces your chance to hit.

Spell Criticals and Critical Strike Chance

Most spells and abilities that deal damage or healing have a chance to cause critical strikes, dealing 100% extra damage or healing. In PvP, this is cut down to a 50% bonus.

Spell haste

Haste reduces the cast or channel time of spells, and decreases the amount of time between ticks for HoTs/DoTs. For HoTs/DoTs, they will continuously gain ticks. If there's not enough haste to grant an entire tick, the last tick will deal a partial amount of damage (more on this below).

Before reading more into this section, it is important to understand a key difference between an effect that increases your casting speed and an effect that reduces your cast time. Spell haste buffs and haste rating will increase your casting speed in a way that will be explained in this section. An effect that reduces cast time simply cuts the base cast time of the spell by the given percentage. Then your spell haste is factored in.

Each source of haste is multiplicative, not additive. Multiple sources of haste are multiplied together, but everything from "haste rating" is considered a single source. To figure out your total haste, take the total amount of haste you have from haste rating, every haste buff (Passive or otherwise). If I have 7% from gear and 5% from a group buff I have a total of 12.35% haste. As a side note, the number displayed in your character sheet does not round up. It is simply truncated to two decimal points.

Now we can figure out how that affects your spells. Take 12.35%, multiply that by 0.01, then add 1. You now have 1.1235, a much easier number to work with. Setting aside other factors like slows, a spell's cast time is the base time divided by your haste. Heal's cast time (without any other effects like Serendipity) will be 2.5 seconds before haste.

2.5 / 1.1235 = 2.225 second cast time.

HoTs, DoTs, and channeled spells are a little more complicated. Not only does haste reduce the time between ticks but it also fits more ticks into the same overall duration, resulting in an increased amount of overall damage from the periodic effect. Most (but not all) periodic effects behave this way. In the past, these spells only gained extra ticks at specific breakpoints. In WoD, it is now more fluid - a periodic effect will continue to partially gain ticks at all points of haste. This means at a certain point of haste, Renew can tick 4.5 times, or 4.339 times. The last tick will be for that partial amount (using these two numbers, the last two ticks would be for 50% damage/healing and 33.9%, respectively).

PvP Resilience

Resilience is a stat designed for PvP content. Resilience reduces the amount of damage done to you by enemy players and their minions, pets, etc. This will no longer be on gear going forward on WoD, but it does still exist on old gear and does still function. This is of no concern at level 100.
Section I Continued

Multistrike

Multistrike is a new secondary stat. This grants you two separate chances for your damage and healing spells to hit again for 30% of the initial value. If I have 5% Multistrike, this means I have two 5% chances each time I cast a spell for it to hit the same target again. Holy Priests are attuned to this stat - they gain 5% more Multistrike rating from gear and their multistrike effects deal 36% of the initial value instead of 30%.

Some effects, like Atonement, will include multistrikes. If this is the case, the effect's tooltip will specify that it is.

Versatility

Versatility is a new secondary stat for WoD. While not increasing your damage as much as other stats do, Versatility offers a unique benefit of a flat reduction to damage taken. Versatility's effects are multiplicative with other effects that either increase damage done or decrease damage taken.

Movement Speed

Movement Speed is a minor stat. It's fairly simple - it is a stat rating that will increase your movement speed and will stack with other effects.

Avoidance

Avoidance is a minor stat. This reduces damage taken from area of effect attacks, which is useful as most dangerous attacks in raids are considered AoE.

Leech

Leech is a minor stat that causes you to be healed for a percentage of all damage you deal or healing you deal to someone else.

Indestructible

This is a new minor stat for WoD. This is more of a passive effect than a rating. If it appears on an item, then that item cannot take any durability damage.
II. Spell, talent, glyph, and racial notes

General Priest Talents, Abilities, and Racials

Angelic Feather: Feathers will persist for 10 minutes. In WoD, they are also changed to prefer the casting Priest over other targets, so be careful if you are trying to cast them for someone else. It will need to be a few good steps away from you.
Cascade: Cascade will not break stealth. The damage or healing value from this spell (As well as subsequent bounces) depends on the distance between the source of the effect and its target. At 0 yards, it deals 40% of its ordinary effect, and scales at a consistent rate as it is traveling. At 30 yards or more, a Cascade bounce will deal its full effect. Cascade will hit a maximum of 31 unique targets and because it inherently has a target limit, it doesn't follow the same rules of AoE caps that the other spells on this talent tier do.
Divine Star: This spell follows normal AoE capping rules - the healing version diminishes after 6 targets and the damage one diminishes after 10 targets.
Halo: Halo will not break stealth. Like Divine Star, this follows normal AoE capping rules. Unlike Cascade, Halo's effect doesn't quite scale at a consistent rate as distance increases. Ghostcrawler has graciously offered a clear and concise explanation of how it works as well as the formula:

The easy to understand way to think of it is that the multiplier on the max damage/healing is 10% at 0yd, up to 40% at 17yd, spikes up to 90% at 22yd, 100% at 27yd, then down to 60% at 35yd. The intent is that it is weak on targets near you, but there’s a sweet spot in a ring from 20yd to 30yd from you, and that the edges of that ‘sweet spot’ are smooth. The actual formula (warning, may seem scary!) is… 0.5 * (1.01)^(-1 * (((Distance-25)/2)^4)) + 0.1 + 0.015*Distance. I’m sure someone can post a graph of that pretty quickly. One thing to note is that the max range is 30yd, but that it includes creature’s hit boxes, so the distance between the caster and a valid target may be slightly larger than 30yd, which is why the formula makes sense out to 35yd.


Prayer of Mending: In WoD, Prayer of Mending is no longer limited to 1 target, but you cannot have more than one on the same target. To avoid this issue, you can cast PoMs toward players in different areas of a room to make them less likely to end up on the same target and overwrite. This spell will heal 5 times in total, but the value in the tooltip has not been correct since WoD launched.
Shackle Undead: This spell works against Death Knights who are under the effects of Lichborne (Often used to break out of priest fears) because they are considered Undead for its duration.
Shadowfiend: Fade can be used to make mobs attack your Shadowfiend instead.
Shadowmeld: Shadowmeld will cause any mid-flight spells to have no effect. Chaos Bolt, Mortal Coil, and Stormbolt are examples of projectiles that will do nothing if you Shadowmeld while they are mid-air.
Spectral Guise: Generally if an enemy is casting a spell at you, Spectral Guise will cause the cast to not finish. Yes, even raid bosses! Use this to your advantage to escape certain raid boss mechanics or in PvP. It is very risky to this spell for bosses that fixate. Chances are it will either not work or cause the boss to immediately refixate, and potentially cause deaths in the process. Although the tooltip suggests that this effect is removed by direct attacks, any damage including random dot ticks will count toward removing it.
Surge of Light: The current incarnation of Surge of Light appears to be procced by more than just casting the spell. For example, sending Halo through a large group of players will proc several times.
Twist of Fate: The tooltip on this talent is not very specific on what may proc it. For example, an incidental Echo of Light tick on somebody that dips below 35% health briefly can proc Twist of Fate.
Void Tendrils: Any damage dealt to a target will also be dealt to the Void Tendrils rooting it. Mobs will not actually attack the tendrils as long as there is something else in range. The tendrils can also be healed. Effects that remove roots will still cancel the effect.

Discipline

Atonement: Atonement's range is measured from the target's actual melee reach. The healing done by this talent is not affected by Grace on its target, but does benefit from other things that increase healing done (Or healing received by the target) such as Archangel. The healing done by Atonement is capped at 1.5 times the base amount, meaning 1.5 times what it would do without any damage modifiers on the target. This cap is applied before healing modifiers are. What this means is that you'll benefit from a target's increased damage taken (Or increase to your damage done) up to a maximum of 50%.
Shield Discipline: Stacks multiplicatively with other modifiers.
Archangel: Does not start and is unaffected by the global cooldown.
Borrowed Time: The buff is only consumed by direct cast spells (Smite, Flash Heal Heal, etc.), not channelled or instant spells.
Divine Aegis: Includes overhealing and has a cap of 60% of the casting priest's health. Multiple priests with Divine Aegis create their own separate Divine Aegis effects when applied to the same target.
Penance: Three hits in total - However only gives one Evangelism stack.
Spirit Shell: Spirit Shell calculates based off of the average throughput of the spell used with it. The basic formula for the shield would look like: Healing Value*(1+Crit Chance)*(1+Mastery Percentage) - This means that spells such as Archangel's critical strike buff still work with Spirit Shell. Spirit Shell caps on any given target at 60% of the casting Priest's health.

Holy

Echo of Light: Multiple applications of this HoT will add on to the remaining amount of healing the previous one had left. Echo of Light is then reset to 6 or 7 ticks (Depending on when it was refreshed) and the healing is distributed amongst those ticks. What this means is if you reapply Echo of Light with a weaker spell and see smaller ticks, it isn't actually because the effect is functioning incorrectly. It means that the sum of the new EoL and the existing EoL was smaller than it was before, thus resulting in smaller ticks. Rolling mechanics such as these are subject to a term called "munching." This means that when two direct heals land and proc EoL simultaneously on one target, there's a chance that the HoT will be a percentage of only one of the casts, instead of the same percentage of the sum of those two casts. This effect cannot crit, multistrike, or tick faster with haste.

Clarity of Purpose: The potency of this spell (how much increased healing it does) is determined by the primary target of the spell. All other players receive the same amount of healing regardless of their HP.
Divine Hymn: Cannot be affected by pushback. This spell is exempt from standard AoE capping rules.
Divine Insight: This version of Prayer of Mending is a completely separate morphed spell from the normal one. If you cast a normal Prayer of Mending and use a Divine Insight proc 4 seconds later, your normal Prayer of Mending will still have 6 seconds left on its cooldown. This version of Prayer of Mending also costs more mana than the normal one, but this is probably a bug.
Guardian Spirit: Does not start and is unaffected by the global cooldown. The absorb / heal from this ability preventing a killing blow is capped at 200% of its target's health.
Holy Word: Sanctuary: This spell will ignore insignificant pets such as Wild Imps, Bloodworms, or Snake Traps. It does not proc Echo of Light and will diminish in healing when hitting more than 6 players.
Renew: The direct healing triggers your Echo of Light HoT. It is also an easy way to proc Twist of Fate when someone dips below 35% health.
Section II Continued

Shadow

Insanity: Insanity's duration is reduced by your haste such that higher levels of haste will not have much impact on the amount of Mind Flay damage you can fit into it. Haste cooldowns like the Berserking racial can partially circumvent this if you pop it after gaining the buff.
Mind Spike: This spell can be cast when locked out of your shadow school due to being a Shadowfrost spell (In other words your frost school remains open) but if you are interrupted while casting Mind Spike you are locked out of both Shadow and Frost, which means Mind Spike is also locked out.
Shadowform: The spell damage increase stacks multiplicatively with other effects. Shadowform only prohibits healing spells, so you may freely use other non-shadow spells without dropping out of form.

Glyphs

Glyph of Dispel Magic: The damage from this does scale with your spell power.
Glyph of Shadow Word: Death: The backlash damage comes shortly after you hit your target, which with precise timing can let you break out of Polymorph or similar effects.

Diminishing Returns

Diminishing returns mostly apply to pvp, but most stun effects are subject to diminishing returns on mobs as well so you don't just CC players and stun mobs endlessly. They come into play when you use the same form of CC on a target repeatedly within 15 seconds after a similar form of CC hit them. Standard CC effects like Psychic Scream and Mind Control last 8 seconds against players.

When a player is hit by a CC effect, like Mind Control, the duration is reduced by half each time up to a maximum of two times. After that, the player becomes immune to that category of CC until 15 seconds after the last time they were hit with that type of CC. Categories of diminishing returns have been overhauled in WoD. As a result, they have become a lot more simplified and the tooltips make it clear what DR each spell will trigger:

Holy Word: Chastise: Disorient
Mind Control: Incapacitate
Psychic Horror: Incapacitate
Psychic Scream: Disorient
Shackle Undead: Disorient
Silence: Silence
Void Tendrils: Root

HoT/DoT Refreshing

When reapplying an existing HoT or DoT on the same target, tick intervals are not interrupted by doing so. This means you no longer have to worry about "clipping" or losing damage as long as you refresh when the effect is about to wear off. Periodic effects are allowed to be refreshed with no loss when the DoT has 30% or less of its unrefreshed duration remaining.

In the past, dots took a snapshot of your stats at the time of application and would tick for that value even after your stats changed. For WoD, snapshotting is gone and tick values are determined by your stats at the time each tick occurs. This means big trinket procs can no longer benefit you after they have expired. Some class/spec specific effects on periodic spells do snapshot, but Priests do not appear to have any of those.
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marry me, Nysem.
Oh boy. Now I can learn stuff and be smart.

<3 Thanks for doing this!
Thanks so much for this!
Awesome thanks man for posting this.
Nysem is an angry priest who refuses to PI gnomes who gave him alot of SP.
Yay for stickie.
Oh boy. Now I can learn stuff and be smart.

<3 Thanks for doing this!


doubt it.
I knew I recognized the name who posted this. :)
Wow, very nice! Thanks very much for updating this.

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