Do spells with options stack when different options are chosen?

Question

Re: commentary on my answer here

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For example, resist energy provides "resistance 5" against one of acid, cold, electricity, fire, or sonic damage; could a creature benefit from another casting of resist energy for a different energy type?

A shield of elemental energy protects a creature against one type of energy damage. Choose acid, cold, electricity, fire, or sonic damage. The target and its gear gain resistance 5 against the damage type you chose.

Are there cases where it would be ruled differently from resist energy?

Answer 1

It Depends Upon the Options

Duplicate Effects

When you’re affected by the same thing multiple times, only one instance applies, using the higher level of the effects, or the newer effect if the two are the same level. For example, if you were using mage armor and then cast it again, you’d still benefit from only one casting of that spell. Casting a spell again on the same target might get you a better duration or effect if it were cast at a higher level the second time, but otherwise doing so gives you no advantage.

The rule points out cases where "you're affected by the same thing multiple times", even giving a spell example in mage armor. The effect of mage armor is an item bonus to AC and potentially saving throws, and casting it again would give exactly the same effect to the character.

It does note that casting a spell again at a higher level might give an enhanced effect, so casting a second more powerful mage armor would give a larger bonus.

Resist Energy

The effect of resist energy is that the target and their gear gain resistance to the chosen damage type. For the same reason as mage armor, resist energy (fire) wouldn't stack with another casting of resist energy (fire) and just the highest level or newest casting would apply.

However, is resist energy (cold) the "same thing" as resist energy (fire)? It grants the target substantially different effects between castings, so I would say this isn't a duplicate effect on the target.

An alternate interpretation could be that the "same thing" is the spell being used, but based on the title of the section that rule comes from, duplicate effects, this seems to be a better way to interpret the interaction.

The final line under duplicate effects about casting a spell again giving no advantage would be explaining the generalized case, for the vast majority spells that always grant the same effect to the user. This is in line with the overarching idea of this answer, that these rules cover duplicate effects instead of duplicate spells.

With Other Sources of Energy Resistance

Another case to consider, what if the target of a resist energy (fire) spell was also wearing a ring of fire resistance? If that target was exposed to fire damage, which of the fire resistance effects would block the damage?

I'd say this is a case where the creature does have a duplicate effect, fire resistance, and that the highest level (depending on heightening) or most recent effect (the continuously applied ring) would likely apply.

Note also that the resist energy protects the target's equipment while the ring does not. This means that even if the ring was stronger or more recently applied, the spell would be protecting the targets gear. Only the duplicated part of the effect would be ignored in either case.

Additionally, a heightened resist energy (fire) that gave fire resistance 10 or 15 would be the "same thing" as fire resistance 5 given by some other source, following the same reasoning as with mage armor. And by the final line under duplicate effects about getting better effects, the higher resistance would apply.

Other Spells/Effects

Spells can do all kinds of things, so this really needs to be evaluated on a case-by-case basis. If the effect of one casting would be the same as any effect currently on the character, then it should be resolved by following the rules for duplicate effects.

Answer 2

RAW, No

The duplicate effect text states:

When you’re affected by the same thing multiple times, only one instance applies, using the higher level of the effects, or the newer effect if the two are the same level. For example, if you were using mage armor and then cast it again, you’d still benefit from only one casting of that spell. Casting a spell again on the same target might get you a better duration or effect if it were cast at a higher level the second time, but otherwise doing so gives you no advantage.

If someone casts resist energy twice on the same target, per the above, the newer effect would apply (or the higher level one if they are at different levels). The "thing" in this instance is the spell - it's clear that they mean that given their example that uses mage armor, also a spell, as the thing. They also explicitly mention that duplicate casting gives no advantage.

The Energy-Resistant rune, while not a spell, does call out that it can stack. While that is probably to override the "no duplicate runes" rule, it's a potential example of the general design philosophy: the ability of something to stack with itself only applies when explicitly mentioned. The relevant text from the rune:

Multiple energy-resistant runes can be etched onto a suit of armor; rather than using only the highest-level effect, each must provide resistance to a different damage type.

Ask Your GM

The same rules also state that the GM has the final say:

If you’re ever uncertain how to apply a rule, the GM decides. Of course, Pathfinder is a game, so when adjudicating the rules, the GM is encouraged to listen to everyone’s point of view and make a decision that is both fair and fun.

Admittedly, one could argue that the "same thing" referenced in the duplication rules refers to a spell plus its effect (so the various permutations would count as different things). I don't think that's the most straightforward reading of the text, but some GMs may not see if that way, and it's their call. It's probably not unbalanced, assuming they don't let you stack the same energy resistance.

The Ambiguous Rules clause from the same rules state:

If one version [of a rule interpretation] is too good to be true, it probably is. If a rule seems to have wording with problematic repercussions or doesn’t work as intended, work with your group to find a good solution, rather than just playing with the rule as printed.

Ruling that resist energy can stack so long as it is providing different kinds of resistance is certainly a buff to the spell, and takes much of the guessing/scouting ahead game out of using resist energy. It definitely makes it more powerful, and there are certain encounters where it might make it significantly more powerful, such as if an enemy different attacks to do different types of energy damage. I think it's a niche enough scenario though that it's hard to argue that this is "too good to be true".