spell penetration

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Does (greater) spell penetration stack with one (or all) of the 5 (greater) spell focuses?

Does spell penetration only serve versus spell resistance or also versus the saving throws as the spell focuses do? (Or vice versa?)

 

I´m pretty sure that they both stack and serve versus saving throws.

 

The spell focus feats are the ones that give saving throw penalties. Spell penetration only works on spell resistance. Or is there more to it?

 

I'm not exactly sure, but I think this is how it works. When a spell strikes a target, first of all it checks the spell's DC against the target's spell resistance. If the spell fails against the resistance, then no other saving throws are required - the spell fails outright. But, if the spell beats the target's spell resistance - which happens at least 90% of the time, since 90% of the critters have no intrinsic resistance anyway - then the target has to make a saving roll (will, fortitude, or reflex). If it fails that saving roll, then the spell works.

So think of it this way. Spell Penetration and Greater Spell Penetration are there to make sure that the spell actually connects; Spell Focus and Greater Spell Focus are there to make sure that the spell actually works.

So they don't really "stack" - they're applied to two separate steps of the spellcasting process.

You're better off investing in Spell Focus, since most critters won't have high spell resistance anyway. Once you've maxed out your appropriate Focus (Evocation or Enchantment are good picks), then work on Penetration so the spells will work on higher-level resistant targets.

 

Grey Magistrate has this pretty much right. The only area where his explanation is wrong is in HOW Spell Penetration is actually punched through. It isn't the DC of the spell VS. the targets spell resistance. It's actually: (D20 + caster level vs. spell resistance). Spell Penetration gives a bonus to that D20 roll. Aside from that, he's right, Penetration and Resistance are a completely different step from Saves and there is no stacking involved with Spell Penetration and Spell Focus.

 

Spell resistance works like this:

1. Target has a spell resistance of X.
2. To hit Target with a spell, a caster of level Y rolls a 20 sided die.
3. If (Y+result+penetration)>=X, then spell is not resisted. If less, then the spell is resisted.

So you see, Spell Penetration is completely different from DC.

 

Just be sure to have Greater Penetration in the Underdark for the duergar and the drow. I remember disintegrating the Guardian dragon too. A good idea is to have Greater Penetration, Greater Focus: Evocation and Spirit of Flame when in the Underdark. Magic doesn't normally work on such creatures. But when it does! Eh! A sight to behold. I suppose I don't have to tell you how my great uber paladin/wizard owned them all?

 

I don't know about the derro thralls, but the duergars, thrall or not, don't get spell resistances. As for the driders, their spell resistance is much lower than that of a drow at the same level; they have only 14 spell resistance. Since spell resistance is essentially caster class level vs. target level, you can be expected to hit most of the time.

 

According to my experiences, do NOT take spell penetration feats at all. They are a minus to YOU, not your enemies!

Why?

A) A vast majority of the enemies you meet (95% or more) have either very low or non-existant spell resistance.

B) The few monsters that actually have spell resistance have boatloads of it, so much that having the spell penetration feat or not doesn't make a difference. You'll have to bring the resistance down with multiple castings of "Lower Resistance" anyway.

C) The only place remaining where spell resistance has an actual effect is when you're bombarding your OWN party (most likely a decoy character with high SR) and having the spell penetration feat will just make your OWN hurt more.

At least I've had much better success at mass area bombardments after I decided to abstain from taking the SP feats.. but YMMV.