[C9] Resistances (BlahR's)

[C9.0] Basic Info

DM Note: This section refers to "BlahR's" (e.g. MR=Magic Resistance, SR=Spell Resistance, etc.). If you are looking for "Resists" and "Immunities" (e.g. "Resist Fire", "Immune Lightning"), see [C8] and [Q15].
Most Resistances are represented as a percentage score, such as "MR 50%". Notable exceptions are SR, PowR, and DR.
I use the term "BlahR" here to mean "a resistance". You can mentally replace "BlahR" with "MR" or "RR" or whatever you have on your character.
Whenever you are hit by an effect of that type, roll the corresponding BlahR (using 1d100, you want to roll your BlahR score or lower). If you make it, you are immune to that effect.
BlahR's are checked only once per effect. If you make it, you are immune to that effect as long as it's running. If you miss, you don't get more BlahR checks later.
You can selectively drop your BlahR against effects to not be immune to them. You don't have to roll MR against a beneficial Heal spell that's hitting you, but if the caster betrays you and reverses it (as a Harm), you will not be able to roll MR against it, unless you have Spellcraft proficiency and know that he's reversing it ahead of time.

[C9.1] Resistance Shifts

Resistances are shifted downwards by high CL (Caster Level), as follows:
Shift = -(CL-12)*5%
So a CL=20 spellcaster has an MR shift of -40% against other people. The shift is never positive (i.e. the shift is 0% for CL=0 to CL=11).

[C9.2] Adding up multiple sources of BlahR's

If you have the same BlahR more than once, you add them by using the following formula:
Total BlahR = (Largest Source)/1 + (Second Largest Source)/2 + (Third Largest Source)/3 + ...
So a character with two sources of MR 40% would have MR 60% (40/1+40/2). BlahR's listed with a "+" in front (e.g. "MR +40%") raw add, they do not use the formula above. So a character with MR 40% and MR +40% would have MR 80%.

[C9.3] Miscellaneous Notes

1. You may "material component" spells for purposes of CL (and thus MR shift), see [S0] Material Componenting.
2. You can use "MR evasion" as a V action to lower MR (or some other BlahR), see [P8.9] BlahR Evasion.
3. Your effects do not get your resistances, all they get is ER (see below). You do not roll MR or aMR vs. Dispel Magic, you roll ER.
4. Sometimes I list multiple resistances together, such as MPIR 30%. This means MR 30%, PR 30%, and IR 30%. I do this because monsters frequently have several types of BlahR's, all with the same values.

[C9.4] Prefixes on Resistances

The following prefixes exist for resistances. They are always lower-case and are before the main resistance type (e.g. "iaMR" for "irreducible anti-Magic Resistance").
The "a" prefix is explained in more detail in [C9.5].
"RC" is "Resistance Cost", see [C9.7] (it doesn't affect play normally).
Abbr. Prefix Description RC
a Anti- Used for anti-effects, such as Anti-Magic Shell. You use aMR to avoid an anti-Magic effect, not MR (or ER). See also [C9.5] Resistance Types below. +2
i Irreducible This resistance does not shift using [C9.1], and cannot be lowered by BlahR evasion [P8.9]. It can still be lowered (by Lower Resistance), ignored, or dispelled. x5
n Non-Ignorable This resistance cannot be ignored by "Ignore BlahR" effects. It can still be shifted [C9.1], evaded [P8.9], lowered (by Lower Resistance), or dispelled/twisted. x3
u Unadjustable This resistance cannot be lowered (by Lower Resistance) or dispelled/twisted. It can still be shifted [C9.1], evaded [P8.9], or ignored. x4
x Infinite This is an infinite percentage of a resistance, see [X] section. "xGR 3%" is the same as writing "GR 3i%" (where i is one level of inifinity). "x" is used here instead of "i" to prevent confusion with "Irreducible (above). +7

[C9.5] Resistance Types

I include "a" (anti) versions of Resistance types below because they sometimes have a special effect.
"RC" is "Resistance Cost", see [C9.7] (it doesn't affect play normally).
Abbr. Resistance Lets you be immune to RC
AR or AllR All This isn't a real resistance, it's shorthand for RMPIWER (Radiation, Magic, Psionic, Innate, Weapon, Effects Resistance). It's BR plus WR and ER. It pretty much covers everything (notable exception being XR and GR). Sometimes I also include CNXR as well, I'll tell you in game if I mean that. (Σ=27)
aAR or aAllR Anti-All This isn't a real resistance, it's shorthand for aRaMaPaIaWaER. It's aBR plus aWR and aER. "AaAR" does occur, it includes everything in AR and aAR. Sometimes I also include aCaNaXaR as well, I'll tell you in game if I mean that. (Σ=39)
BR or BlahR Blah This isn't a real resistance, it's shorthand for RMPIR (Radiation, Magic, Psionic, Innate Resistance) (Σ=14)
aBR or aBlahR Anti-Blah This isn't a real resistance, it's shorthand for aRaMaPaIR (all the Anti-'s of BlahR). "BaBR" is fairly common (includes everything in BR and aBR). (Σ=22)
CR Charm Enchantment/Charm school; Charm sphere; some charm-based racial and magic-item abilities 1
aCR Concrete Some technological effects use aCR, see [Q8] 3
DR Damage [This is the same as 3rd Edition DR.] Like WR, but not a percentage. It is written as A/+B, where "A" is the amount of damage (per attack) reduced unless he counts as a +B or better weapon. An "all" instead of "A" means all damage is removed (same as "+B or better weapon to hit" seen in 1st and 2nd edition AD&D). A "-" (dash) instead of "+B" means the DR applies to any weapon (regardless of plusses). 6
aDR Anti-Damage Like aWR, but not a percentage. It is written as A/+B, where A is the amount of damage (per attack) reduced unless he counts as a +B or better weapon. A "-" (dash) instead of +B means the aDR applies to any non-weapon attack (regardless of plusses). 8
ER Effects This protects your effects from Dispels, Twists, DMZ's (Dispel Magic Zones), etc. Roll the ER, and if you make it, your effect is not dispelled. Does not protect you from Anti-Magic / Anti-Psionics / etc. 7
aER Anti-Effects Damaging Shields and Effects (roll your aER, if you make it, you don't take damage or negative effects back from a Fire Shield or whatever the enemy is running on himself) 9
GR Godly Godly effects; Demigod group effects; see [X] section; GR is very rare. 14
aGR Anti-Godly Anti-Godly effects; Atheist effects; see [X] section; aGR is very rare. 16
IR or InnR Innate Innate (Racial) abilities; Rogue abilities (such as Pick Pockets) 5
aIR or aInnR Anti-Innate Anti-Thief class abilities 7
MR Magic [This is the same as 1st/2nd Edition MR.] Wizard spells; Priest spells; most magic items; magical traps (but out-of-phase traps frequently give no BlahR at all) 3
aMR Anti-Magic Anti-Magic Shells (but not DMZ's, that would use ER); Anti-Magic-User spells 5
aaMR Anti-Anti-Magic Anti-Anti-Magic Shell (which would stop Anti-Magic-User spells) 7
NR Natural Natural effects (e.g. a natural Lightning Bolt from a normal rain cloud); some Druidic effects 5
aNR Necromantic Necromancy school; Necromancy sphere; Energy drain (Negative levels); Stat damage; Degeneration 7
aaNR Unlive Unlive effects (Positive levels); Undead can roll aaNR vs. Turn Undead. 9
PR or PsiR Psionic most positive numbered Psionic Frequencies; monster abilities that are mental / psionic-like; psionic traps 4
aPR or aPsiR Anti-Psionic Anti-Psionic Shell; most negative numbered Psionic Frequencies 6
aaPR or aaPsiR Anti-Anti-Psionic Anti-Anti-Psionic Shell (which would stop negative Psionic frequencies) 8
PowR Power [This is the same as 3rd Edition PowR.] Like PR, but not a percentage, instead, the caster rolls 1d20+CL to overcome the PowR. It is not shifted by [C9.1]. 4
RR Radiation [This is the same as 1st Edition RR.] Radioactive effects; Psi9,18,27,45,54,72 2
aRR Anti-Radiation Psi(-9),(-18) 4
SR Spell [This is the same as 3rd Edition SR.] Like MR, but not a percentage, instead, the caster rolls 1d20+CL to overcome the SR. It is not shifted by [C9.1]. 3
TR or TechR Technology Technology (see [Q8]); Bioware; Cyberware; High Technology Weapons (Lasers, etc.); Psi8 8
aTR or aTechR Anti-Technology ? 10
WR Weapon Weapon attacks (non-weapon attacks such as claws are covered by aWR below); Weapon flags (e.g. Vorpal) unless they are the duplicate of an effect (e.g. a Prismatic Spray Brand would use MR, not WR); most mechanical traps (but some such as pits give no BlahR at all) 6
aWR Anti-Weapon Non-weapon (Natural) attacks (claws, bite, tail, etc.); Martial Arts maneuvers; Psi0 8
XR Spirit / Concordant Artifacts; Relics; Concordant group effects; XR does not cover Ego (see [C8]), however (no resistance covers Ego) 9
aXR Anti-Spirit / Anti-Concordant Anti-Concordant Shell 11

[C9.6] Suffixes on Resistances

The following suffixes exist for resistances. They are always completely spelled out and replace the "R" at the end of the resistance (e.g. "MDeflection" instead of "MR").
Suffixes are rather rare and exotic; I don't use them often because they add a level of complexity unneeded for the game effect.
"RC" is "Resistance Cost", see [C9.7] (it doesn't affect play normally).
Suffix Description RC
Absorption This is BlahR that cannot be dropped. You must always roll the BlahR, even against beneficial effects. x0.75
Armoring This is written as a flat number, like "MArmoring 25". You take 25 less damage from magical effects. MArmoring is still shifted using [C9.1], at 5 per CL above 12. Note that "DR" is quite similar to "WArmoring". "iWArmoring (number)" is the common "-(number) per attack" seen in many effects. x1
Deflection Instead of being immune to the effect, you deflect it randomly outwards. There is a 10% chance (per other creature in your group) that another creature in your group is struck by the effect. Which creature is struck is determined randomly. Deflection ignores the "Can't be Targetted" flag. Note someone else will always be struck if there are at least 10 other people in your group. The struck target rolls his BlahR against the effect. If this somehow forms an endless loop, there is a rift (see Reflection below) which includes everyone in your group, and the original caster too (even if he isn't in your group). x2
Reflection Instead of being immune to the effect, you reflect it back on the caster. The caster does not have time to drop the effect before it hits him, but he can roll BlahR's against his own effect. Reflection ignores the "Can't be Targetted" flag. If an effect endlessly reflects between two people, they both enter a rift into the Astral (Wizard spells) or Positive Energy Plane (Priest spells) and are Capital S Stunned. The original caster cannot be immune to the Capital S Stun component, but the other person can use immunity to Capital S Stun if he has it. x3

[C9.7] Resistance Costs

DM Note: This rule can largely be ignored when using BlahR's, as it doesn't affect how BlahR's actually function.
Spell Research:
The "RC" (Resistance Cost) factors given in [C9.4] through [C9.6] show the relative strength (or difficulty in getting) the relevant power type (or resistance).
The "Dispel" and "Reverse" spells use RC to determine SL (Spell Level). So "Dispel Magic" is a 3rd level spell (since the RC for Magic is 3), and "Reverse Anti-Technology" would be SL=10.
"Identify" spells use RC-2 (e.g. "Identify Concordant" is a 7th level spell). However, the actual spell "Identify" (by name) does cover Psionic items.
Resistance Mutation:
There are times you can change your BlahR's from one type into another. The easiest way to do this is with the "Pearl of Mutation" magic item.
The RC factors give the relative costs of the BlahR's. So, you can convert MR 50% (total RC=150) into PR 37% (150/4=37.5, dropping the fraction).
In this one rare case in the Collective, you add RC factors before you multiply (for prefixes and suffixes), so iaMR is (3+2)*5=25, not 3*5+2=17.
If you have several multipliers, add them up and subtract 1 for each additional source (so all three prefixes of "iun" costs x10).