Spell Penetration
Posted on February 2nd, 2009 by Lithanial under General Tips, PVP, World of Warcraft, WotLK
Spell penetration always has and will likely always remain a highly misunderstood statistic on peoples equipment. Before WotLK pretty much nobody deliberately sought it out, treating it as the red headed stepchild of itemization that seemed to have no use.
With WotLK however things seem to have changed as many classes have come to realise just how important it is for them in PvP; a movement that has mostly been spearheaded by the Death Knights unique mechanics making certain things stand out. To understand just how important spell penetration is though you need to have an understanding of how spell resistances work.
Every spell and melee strike in PvP has a basic 4% chance to miss completely, this can then be further increased by racial traits to 6% or even further with a few classes talents. This basic miss rate works exactly like your chance to miss in PvE content and can be countered with hit rating; for a death knight, a missed attack does not fully consume a rune but instead puts it on a 1.5 second cooldown only.
Separate to this basic miss chance is a spell resistance check which can work in one of two ways depending upon the skill used. Damaging spells or elemental melee attacks that only deal damage come under the rules of “partial resistance” while spells with non damage based effects such as polymorph, entangling roots and chains of ice come under the resist rules of “binary resist”.
Attacks which fall under the rules of partial resistance have a chance to have anything from 0-100% of their damage resisted; increasing in 10% increments. The chances for this damage mitigation are dependent on how much resistance the target has; the highest effective level of resistance against a level 80 target is 400 which will yield average mitigation of 75%.
A class such as a Paladin is able to activate an aura which will grant them and their allies 130 shadow resistance which gives a proportional amount of average damage mitigation against partially resistible spells that works out around a 24% damage reduction. This amount of damage mitigation is very significant and can be crippling when attempting to burst down a target.
Far more crippling however is spell resistances effects upon binary spells. Since a binary spell generally does little or no damage a partial resist would do little to protect you from its effects; instead what happens is the average damage reduction that would have applied to a partially resistible spell gets added as additional miss chance.
Taking the example above a binary shadow spell would have an extra 24% chance to miss its target completely should it be under the effects of a Paladins aura. For classes such as Priests who rely on long cooldown abilities such as psychic scream landing for their survival a resist of this nature can be catastrophic as they cannot simply cast the spell again if it does not work. Similarly a spell cast by a Death Knight that is resisted in this manner will fully consume its runes placing them on a full 10 second cooldown, making resists fully capable of completely crippling their rotation.
Considering the damage such low amounts of spell resistance can do it is well worth gathering around 130 spell penetration should you decide to seriously PvP; especially for classes that are reliant on binary spells with cooldowns.
Wonderful!
Just what I was looking to read ^^ Going to go enchant my cloak with Spell Penetration now 
P.S. First?
So basically you’re saying that spell pen negates resistances and spell hit negates the chance we have to miss them completely? How do the two stats work together? Do they work together?
I assume spell penetration effectively reduces the target’s resistance to your spells cast on them? It’d help to have a more detailed explanation of what it actually does. For example, does 130 spell penetration mean that a pally with the aura has 130 (from aura) – 130 (from spell pen) = 0 effective resistance?
yes. It decreases opponents’ resistance
yes, spell penetration works 1 for 1, but does not reduce their resistance past 0.
for example: if you meet another player on the field of battle and they have an unimproved Mark of the Wild which grants them 54 spell resist.
if you had 54 spell penetration, your spell will proceed to hit the target as if he had 0 spell resist.
however, if you had 100 spell penetration, it will still hit as if he had 0. so more is not nessarily better..
somewhere between 40-80 spell penetration would probably be sufficent for PvP. Useless in PvE however.
The above is true, however, you want to always anticipate them having a paladin in their group so having 140-160 spell pen is never a bad idea
Ask spriests, they’ll tell you that many of them actually valued spell penetration before wrath. 30-50 Spell pen was what we needed pre-wrath, currently 90-110 should be fine.
For most results, I would say 130 Spell Pen for PvP. That negates the Pallies Frost/Shadow/Fire Resist Auras, and the Priests Shadow Resist Spell, which all do 130 Resist. Just my .02
Im a druid… if i cast Cyclone on a target, and it is resisted, does that still cause Deminishing Returns? or is it considered a miss and will still hit for the full duration on next attempt?
a resist triggers diminishing returns, but a miss doesnt
Sp spell Pen is equal to Armor pen for melee.
How does a players def skill factor into this? not def from armor but the actually skill that each character has.
Edit:
So Spell Penetration is equal to Armor Penetration for melee?
spell pen reduces the chances of partial or full resists, where as hit is actually hitting the target.’
remember you have to hit and then dmg the target, hit is to make the contact and then the 2nd calculaition comes into play where you need to actually do the dmg. armour and resistance reduce these and armour pen and spellpen increase these.
Please correct me if i am wrong, but if i am competing with oponents with usually no Resistances to Fire magic Spell penetration will be useless for me ?
I ask this becuase i do low lvl BG’s … and want to know if Spell penetration would benefeit my Fire Mage.
Yes daniel, if they have zero resistance already spell pen will do nothing for you, it only negates positive resistance