First we separate all spells into two categories: binary and non-binary. Resists work differently for each so it is important to know which method applies to each spell.
- Binary spells are spells that have two outcomes (which is where the name comes from): they either hit for full effect or miss completely. The binary spells in WoW are those that have a non-damaging component to it, such as Frostbolt (snare effect) and Death Coil (leech effect). These spells cannot be partially resisted, they either hit for 100% of their damage or they miss. All of our Affliction spells are binary on application.
- Non-binary spells are spells that only have a damaging component. Shadow Bolt is a non-binary spell since it only does damage. Immolate is a non-binary spell since both the direct damage and DoT portions only do damage. Non-binary spells can be partially resisted.
- PvP Resistance:
vs +0 level player (same level): 4%
vs +1 level player: 5%
vs +2 level player: 6%
vs +3 level player: 13%
And so on (+7% for each additional level)
- PVE Resistance:
vs +0 level mob (same level): 4%
vs +1 level mob: 5%
vs +2 level mob: 6%
vs +3 level mob: 17%
And so on (+11% for each additional level)
The highest level for players in the game is currently 70. The highest level for mobs in the game is currently 73. Chance to hit is capped at 99%. For the following examples, we will assume you are a level 70 player fighting a level 73 mob.
Non-Binary Spells:
First Roll: The first roll is based on the level difference between you and your target (aka your "chance to hit"). Since the mob is three levels higher than you, you will hit 83% of the time and miss 17% of the time (see the PvE table above). You can increase your chance to hit for this check through +hit gear. Let's say you equip +6% hit from gear. You will now hit for 83 + 6 = 89% of the time and miss 11% of the time. Note that if you miss during this roll, it will say "RESIST" even though your spell wasn't technically resisted.
Because of the 99% hit chance cap, for PvE you would need +16% hit from gear for maximum effectiveness. Any more than that and the extra +hit is wasted. For PvP, at level 60 you would only need +3% hit gear to maximize your hit chance.
Second Roll: The second roll is based on your level and the resistance rating of your target. The "resistance rating" is how much Shadow Resistance he has, for example. During the second roll, non-binary spells can be resisted for 0% (full damage taken), 25%, 50%, 75%, or 100% (full damage resisted) of their regular damage. Here is a formula to calculate "average resistance" (how much damage you or your target will resist, over time).
- Formula
Target's Average Resistance = [Target's Resistance Rating / (Caster's Level * 5)] * 0.75
The Target's Resistance can be negated through -resist gear and curses such as CoS and CoE. By using -resist gear you can decrease the amount of damage resisted by your target. Using Ogdin's resistance analysis mod GLOCK (http://www.curse-gaming.com/en/wow/addo ... lysis.html), you can figure out how much each boss or mob's resistance rating is and, using the formula above, figure out how much -resist gear you should use on specific encounters.
Note: It has been tested that mobs will gain an additional 8 spell resistances for each level above you (so +24 resistance rating for level 63 mobs). These level based resistances cannot be negated by any means, resulting in about a 5.5% reduction in overall dps over a fight. It has not been confirmed whether this is a bug or working as intended feature, but it apparently was introduced in patch 1.09 when negative resistances were removed. These additional resistances factor into the formula for the Second Roll. For more reading on this somewhat controversial subject, read:
- http://forums.subcreation.net/viewtopic.php?t=482
http://forums-en.wow-europe.com/thread. ... en&T=132218
Binary Spells:
One Roll: There is only one roll for binary spells since it either hits for full effect or misses completely. There are no partial resists involved so it's somewhat less complicated to calculate compared to non-binary spells. This roll is based on your the level difference between you and your target (aka your "chance to hit") and the resistance rating of your target. Chance to hit and resistance rating were both previously explained in the Non-Binary Spells section above.
- Formula
Chance to land your binary spell = (Chance to hit) * [100 - (Target's Resistance * .25)]
You can reduce the chance of your target to resist your binary spells through +hit gear and -resist gear. Since most of our binary spells are also Affliction spells, you can also put points into the Suppression talent to reduce chance of resists.
It seems that Suppression is able to transcend the 99% hit cap (although this may have changed in a recent patch). In PvP, you have a 96% chance to hit your same level opponent. If you have no +hit gear, but have five points in Suppression, your chance to hit increases to 106%. If your target has less than 22 resistance rating, you will land 1.06 * [100 - (22 * .25)] = 100% of your Affliction spells on him.
DoTs:
DoTs are binary spells whose ticks can be partially resisted. This is contrary to the popular misconception that DoTs always hit for 100% damage. They are binary in that the initial cast of the spell either hits the target or it is resisted, and this is calculated as a binary spell. After the DoT lands, each tick is subject to the non-binary "Second Roll" - that is, the tick can be resisted for 0%, 25%, 50%, 75%, or 100% damage. Since the target would require a pretty good amount of shadow resistance for this to happen, these partial resistances don't occur frequently.
This effect specifically applies to Corruption, Curse of Agony, and I assume Curse of Doom. The ticks of Siphon Life are binary (they have a non-damaging component: leech), so Siphon Life ticks cannot be partially resisted.
Are -resist items helpful in raids?
-resist items are not really as helpful as it would initally seem. -resist items directly reduce the chance for your targets to partially resist non-binary spells and miss binary spells, by basically subtracting their resistance rating. However, warlocks already have built in debuff spells that lower the target's resistances by 75 (CoS and CoE), which is more than the resistance level of most raid mobs in the game.
The game also addes 8 resistance rating points for each level the mob is higher than you, up to 24 for level 63 mobs. These level based resistances cannot be negated by any means, including -resist items. Read "How do resists work?" above for more information on this subject.
So why are they in the game, you may ask. Well, obviously there are raid mobs with resistances higher than 75. In those cases -resist items would be effective. Secondly, people speculate that -resist items were meant more as a PvP stat. This would explain why nearly all of the -resist items are obtained either as battleground rewards (Rune of Perfect, Don Rodrigo's Band), or part of the AQ40 set pieces. Also, not all classes have an innate resistance debuff spell like Warlocks, so these items may be more suited for other classes such as mages, priests, and shamans.
In summary, -resist items are useful in reducing your chance to miss and be resisted, just not as much as you probably think it is.
Can resists go into the negatives using curses or -resist items?
No. However, you will encounter certain mobs that have innate vulnerabilities.
