Pax said:
ST is guaranteed, SR is not. With items, PRC abilities, and feats, it's actually possible to have 1d20+level+10 for penetrating SR; so the Cleric's Level+12 SR is penetrated on a roll of 2 or better. *shrug*
We are talking about a normal game, right? So there may be one NPC in the entire game with that level of spell penetration. Every other NPC is stuck with SP and possibly GSP.
The other +6 that you are getting from mysterious sources does not really matter, IMHO.
Besides, the bead of karma boosts the cleric's SR by four. I also forgot the orange ioun stone. I'd add in spell girding (effectively making it +2SR), but then I might have to add something from another non-core source, so I'll leave that out.
This is also neglecting that most NPCs are lower caster level in the first place. (Unless your campaign is abnormal)
So say a PC cleric has 12 +cl +5 (bead of karma and orange ioun stone, both core)
The NPC would have 1d20 +cl +4 (SP and GSP)
17 to 14.5 if their caster levels are the same. PC Cleric wins 57.5% of the time. A fifth level spell that has that level of protection versus almost every attack spell is pretty stinking good. Better than the one spell you get from spell turning. So if you get targeted by two spells a day while SR is up, you are a bit better than ST, three and you are superior.
At high levels, are you targetted by three or more spells in 38 minutes? Heck ya!
All from a fifth level spell.
That's also assuming that the caster levels are the same. (Which would mean one caster at your level for a balanced encounter. Two casters of your level would be overpowering.) Most encounters have casters that are 1 or more caster levels lower than the PCs.
... without support from Nondetection.
Of which a PC cleric has a better than average chance of ignoring, considering a PC is generally a higher caster level than NPCs, the bead of karma, and the orange ioun stone.
And anyway, True Seeing says it sees through illusions. Mirror Image creates illusions. Nondetection effects a creature or an object, not the mirror images surrounding you. (At least, that's my interpretation of it.)
Hence why I deem mirror image obsolete.
3.5 SRD said:
Nondetection
The warded creature or object becomes difficult to detect by divination spells such as clairaudience/clairvoyance, locate
object, and detect spells. Nondetection also prevents location by such magic items as crystal balls. If a divination is attempted
against the warded creature or item,
Mirror Image
Several illusory duplicates of you pop into being, making it difficult for enemies to know which target to attack. The figments
stay near you and disappear when struck.
Mirror image creates 1d4 images plus one image per three caster levels (maximum eight images total). These figments
separate from you and remain in a cluster, each within 5 feet of at least one other figment or you. You can move into and
through a mirror image. When you and the mirror image separate, observers can’t use vision or hearing to tell which one is
you and which the image. The figments may also move through each other. The figments mimic your actions, pretending to
cast spells when you cast a spell, drink potions when you drink a potion, levitate when you levitate, and so on.
Enemies attempting to attack you or cast spells at you must select from among indistinguishable targets. Generally, roll
randomly to see whether the selected target is real or a figment. Any successful attack against an image destroys it. An
image’s AC is 10 + your size modifier + your Dex modifier. Figments seem to react normally to area spells (such as looking
like they’re burned or dead after being hit by a fireball).
While moving, you can merge with and split off from figments so that enemies who have learned which image is real are
again confounded.
True Seeing
sees through illusions,