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Do you roll a caster level check for spell resistance once per spell, and then apply it to each creature separately, or do you roll a separate caster level check for each affected creature?

The tables I have played at have always rolled once for each affected creature, but I'm starting to question that. Although not 3.5, here is a interesting Pathfinder discussion on the matter, which may apply.

SevenSidedDie
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Zarus
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1 Answers1

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On average, in the long run, both approaches are the same, since it’s the same roll one way or the other.

Rolling just once per spell will result in a swingier result: you are closer to an all-or-none situation rather than possibly getting some but not all. It’s also faster in play, particularly when there are a lot of targets.

But if you roll enough times with either method, eventually your results will tend towards the same average. Rolling more (per creature) will tend towards that average more strongly.

Anyway, the official rule is

If your spell is being resisted by a creature with spell resistance, you must make a caster level check (1d20 + caster level) at least equal to the creature’s spell resistance for the spell to affect that creature.

This very much describes a pair-wise situation: a creature resisting a spell. You are rolling a check against that creature’s SR. If there is another creature also resisting that spell? Roll a separate check against their SR. (Note that Pathfinder uses absolutely identical language for this.)

As a result, rolling just once per spell is a houserule, probably intended to speed up gameplay.

KRyan
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  • What would your stance be on this quote from the dark wanderer? " The following one line, however implies otherwise:

    "The defender's spell resistance is like an Armor Class against magical attacks." All vs-AC attacks that hit an area, like the X-laser, shotgun, and automatic weaponry, roll once for all creatures in the field of fire." He goes on to state that either interpretation is valid, RAW. Here is the link. https://rpg.stackexchange.com/questions/64347/aoe-spells-and-multiple-creatures-with-sr

     – Zarus Aug 16 '18 at 19:42
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    @Caldrun He is wrong: “like” does not mean “behaves exactly the same as for all purposes and obeys every rule of,” it’s just a description that there is a conceptual similarity between the two, which may be helpful in understanding how it works and what it’s for. – KRyan Aug 16 '18 at 19:45
  • Would you use the "one roll" interpretation as a house rule when dealing with 20 or more enemies as part of a single AOE spell? – Zarus Aug 16 '18 at 19:52
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    @Caldrun Probably, but it’d depend on the specifics. I don’t tend to find that these games handle large numerical disparities well in combat, though, and tend to almost-exclusively use combats between parties of similar sizes. – KRyan Aug 16 '18 at 19:53
  • Perhaps any spell (e.g. Surge of Fortune) or effect that can seriously affect a single die roll would make the "one roll" interpretation overpowered? – Zarus Aug 16 '18 at 20:05
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    @Caldrun Yeah, it would definitely affect balance in such a case. – KRyan Aug 16 '18 at 20:06