How are Fireball attacks on Iron Golems resolved?

Question

The party was in Curse of Strahd this evening and encountered two iron golems.

A helpful NPC first cast lightning bolt, damaging both of the golems.

The PC evoker then cast fireball on the golems, potentially healing them, but for how much?

Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.

The golems have:

Damage Immunities Fire

and

Fire Absorption. Whenever the golem is subjected to fire damage, it takes no damage and instead regains a number of hit points equal to the fire damage dealt.

Between these three effects (saving throw against spell damage, immunity to damage, and absorption of damage), what is the order of application?

Was there no effect from the fireball, did it heal them for its full rolled damage amount, or did the amount it healed them by depend on whether or not they made their saves?

Why should the Golem have both Immunity and Absorption, doesn't each obviate the other? If the Immunity is applied first, the Golem takes no damage and so Absorption is not triggered. If Absorption is applied first, the Golem takes no damage and so Immunity is not triggered.

If Immunity is applied before Absorption, the ordering of the Saving Throw does not matter. But if Absorption is applied before Immunity, how much the Golems will heal depends on whether the saving throw is applied before or after the Absorption.

Absorption says that it is triggered whenever the golem is "subjected to fire damage". I do not think that "subjected to damage" is a defined game term. The natural English definition of "subjected to" could be interpreted as "whenever it actually takes damage [after the saving throw]" or "whenever it is at risk of taking damage [before the saving throw]", so no help there.

For a saving throw (emphasis mine)

A saving throw--also called a save--represents an attempt to resist a spell, a trap, a poison, a disease, or a similar threat. You don’t normally decide to make a saving throw; you are forced to make one because your character or monster is at risk of harm.

If you make a saving throw when you are "at risk" of harm, that to me implies the save is made before the damage is applied, or in this case, absorbed.

So, my interpretation would be:

1. Fireball damage is rolled.
2. Golems attempt their saves. Successful saves halve the damage.
3. Absorption means no damage is taken, and instead hp are regained. More hp are regained if the save failed than if it succeeded.
4. Immunity is never triggered since they did not take damage.

Is this correct?

Answer 1

Your Interpretation is Correct

In D&D 5e specific beats general. That is:

If a specific rule contradicts a general rule, the specific rule wins.

In this case Damage Immunity: Fire is a general rule that applies to many creatures, allowing them to take no damage from fire. Fire Absorption is given in the monster's statblock and specifically describes how Iron Golems interact with fire damage. This is the more specific rule and the one your should follow:

Whenever the golem is subjected to fire damage, it takes no damage and instead regains a number of hit points equal to the fire damage dealt.

What about the saving throw?

Immune creatures still make savings throws so the Iron Golem would make a saving throw as normal. It would benefit the Iron Golem to fail this save, however technically they aren't allowed to do this, but many tables allow it (see: Can you choose to fail a saving throw?). Additionally the saving throw will actually be made at Advantage due to the Iron Golem's Magic Resistance feature:

The golem has advantage on saving throws against spells and other magical effects.

The wording of the fireball spell gives us the order of events:

(...) A target must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.

So first the Golem makes a dexterity saving throw (at advantage), then the damage (8d6) is calculated. On a failed save the target is 'subjected to' the full amount. On a successful save they are subjected to' half as much damage. In either case the Golem takes no damage and instead regains HP equal to the damage they would have taken due to Fire Absorption.

Also note that the order of the saving throw and damage calculation do not actually matter. The damage applied/taken/subjected upon the target occurs after the saving throw is made and Fire Absorption kicks in upon the applied damage.

Regarding the dual listing, my assumption is that the immunity is listed in addition to Fire Absorption to make it less likely DMs will forget about it. I would often only check the Damage Immunities/Resistances section of a stat block, having it there is useful although slightly redundant.

Answer 2

The intent is obvious.

Your interpretation is obviously correct. Obviously the feature does something, so there is no need to entertain the idea that it does nothing.

So naturally, we conclude that Fire Absorption works as described, being resolved prior to fire immunity. This answer is similar to another answer of mine, where I give more detailed exposition on reading the rules this way: Do features that say they let you see invisible creatures and objects actually let you see invisible creatures & objects? :

It's quite simple, really. The intended function of these features is so abundantly clear, that any argument that concludes that they do nothing can be dismissed out of hand.

In fact, this principle applies in general. If you read a feature, and know what it is supposed to do, but you determine that the feature actually does nothing, you can know without any doubt that your conclusion is wrong.

You’re on the right track - obviously the feature is supposed to work as you have described.

Answer 3

The answer is that

RAW cannot resolve this problem and you are sufficiently correct

. You must use RAI and your best judgement. Don't forget the Iron Golem's Magic Resistance which would give it advantage on the saving throw when you use your method to resolve the conflict. The significance of Magic Resistance becomes clear from an examination of previous editions of D&D.

The Iron Golem used to reduce a portion of damage based on the number of dice of fire damage. 2e MM p.166

Magical electrical attacks will slow it for 3 rounds, and magical fire attacks actually repair 1 hit point of damage for each hit die of damage it would have caused. All other spells are ignored.

3.5e MM p. 136-137 (Immunity to Fire is not a listed quality)

Immunity to Magic (Ex) An iron golem is immune to any spell or spell-like ability that allows spell resistance. In addition, certain spells and effects function differently against the creature, as noted below. [...] A magical attack that deals fire damage breaks any slow effect on the golem and heals 1 point of damage for each 3 points of damage the attack would otherwise deal.

MM 4E p. 134-135 (no immunity and no fire absorption???).
The Iron Golem returned to absorbing fire in MM 5E p.170

So the Iron Golem is intended to absorb fire damage ostensibly from magic and the prevalence of Fireball in all editions of the game suggests that the intention was for the Iron Golem to heal from Fireballs cast by adventuring parties (but never for the full amount of the Fireball). Based on the history of the Iron Golem, I recommend that the Iron Golem heal from the Fireball regardless of the outcome of the saving throw or of magic resistance or fire "immunity".

I further recommend that only magical fire heal it, remove Fire Immunity from the stat block, and simplify the damage healed to 1/2 of the damage that might've been dealt from a magical fire effect. I recommend these rulings because the RAW are clearly a mistake, these rulings provide a simple way to meet RAI without over complication, and these rulings remain consistent when other magical effects are associated with the same saving throw associated with the fire damage. It also makes it a simple matter to add a slow from magical electric damage such as from Lightning Bolt which is removed by a magical fire effect such as Fireball, if you ever have the desire to make iron golems a more interesting combat encounter in other games you run.

To Sum Up You Could Simply:

Resolve the damage roll for the Fireball and heal the Iron Golem for half of the rolled damage.

A saving throw is only necessary if there are other consequences from a failed save besides Fire damage and don't forget that the Iron Golem has Magic Resistance which can give advantage on some saving throws.