How do you handle simultaneous damage when one type is absorbed and not the other?

Question

Say a wizard sees something a group of large figures lumbering towards him/her. The wizard is overly paranoid about being outnumbered so they drop a Meteor Swarm spell on them. However, it turns out the group were all Iron Golems. According to their stat block they will absorb the fire damage from the meteor swarm, but take the bludgeoning damage from the spell as HP loss.

How do you resolve the damage taken? If you apply the fire damage first and they are at full HP they won't heal from it, then the bludgeoning damage will hurt them after that.

If you apply them simultaneously then I'm still not sure. I can't decide if simultaneous means subtracting the fire damage from the bludgeoning damage, or if you apply each based upon the current HP of each Iron Golem then resolve the difference. eg. If they are at full HP they'd get +0 from the fire damage and -20d6 from the bludgeoning damage. Adding them together then you end up with 20d6 damage.

Answer 1

Xanathar's Guide to Everything has guidelines for simultaneous effects; the person whose turn it is determines the order of simultaneous events

The meteor swarm spell states:

[...] A creature takes 20d6 fire damage and 20d6 bludgeoning damage on a failed save, or half as much damage on a successful one [...]

It gives no indication of these happening at different times, and so we will assume that they happen simultaneously. In this case we can look to Xanathar's which states:

Most effects in the game happen in succession, following an order set by the rules or the DM. In rare cases, effects can happen at the same time, especially at the start or end of a creature’s turn. If two or more things happen at the same time on a character or monster’s turn, the person at the game table — whether player or DM — who controls that creature decides the order in which those things happen. For example, if two effects occur at the end of a player character’s turn, the player decides which of the two effects happens first.

In the case here we have two effects (fire damage and bludgeoning damage) happening at the same time. It is (presumably) currently the Wizard's turn and thus they get to determine the order of any simultaneous events, this means that they (presumably) would choose to have the fire damage inflicted first and then the bludgeoning damage afterwards.

Answer 2

Apply them simultaneously

The spell does 20d6 bludgeoning damage and 20d6 fire regain - roll both sets of dice and take the fire from the bludgeoning. If its positive they suffer that much damage, if its negative they regain that many hit points (up to their maximum), if its exactly equal then nothing happens.

Answer 3

The rules are unclear, so the GM decides

The rules (aside from Xanathar's) give no real resource on the ordering of simultaneous damaging effects. We can see that they are simultaneous because meteor swarm states:

[...] A creature takes 20d6 fire damage and 20d6 bludgeoning damage on a failed save, or half as much damage on a successful one [...]

It does not indicate that they are at different times and in particular it says they take fire and bludgeoning damage, not one and then the other. The GM has a few options then as the rules are silent:

1. Apply one and then the other anyways:
   This is still an option; however, this does make the spell either useless, or very useful depending on the ordering, as you've addressed.
2. Apply them simultaneously:
   Unfortunately, there's no real way to actually do this in the rules. And simultaneity is generally avoided. Perhaps you could subtract the fire damage from the bludgeoning; healing if the result is negative, and dealing damage if it is positive, but this is not supported by the rules.
3. Take the average of the two orderings (fire first, and bludgeoning first):
   This doesn't have any basis in the actual written rules, but it does avoid the "all-or-nothing" feel of choosing an ordering.
4. Some other option of your choice:
   Since we're already in GM Fiat territory, this is always going to be an option.

Answer 4

(I present this as an examination of this idea, not a recommendation.)

Attempt to decide based on the spell description if one of them happens slightly sooner

Bludgeoning can happen near-instantly (a shock wave crushing or even ripping material, like in a real-world explosion).
Heat takes a few moments to do its damage. Unless the target creature's flesh is magically heated / turned to char directly, a blast of hot air takes some time to conduct heat into skin. Or into an Iron Golem.

But radiant heat (infrared photons) is absorbed pretty much directly, and perhaps much magical fire damage is mostly from radiant heat, not superheated air. And the speed of light is higher than the speed of a shockwave.

For Meteor Swarm, the description sounds like an explosion.

Blazing orbs of fire plummet to the ground at four different points you can see within range.

So the orbs are of fire, not like a real-world meteorite (a rock which hits the ground really hard). You're not literally getting hit by a large hypersonic rock; that would be even more lethal. (And wouldn't explain applying everywhere in a 40ft radius.) The bludgeoning comes from an explosion as the meteor hits the ground. Most of that is from a one-time shock wave, not ongoing buffeting.

My initial thought was that the fire damage would then follow as fiery air or a wave of magical fire reaches targets.

But the fire damage could easily be mostly radiant heat and be delivered in about as quick a burst as the bludgeoning.

Also, this doesn't explain the spreading-around-corners property. So maybe each Meteor really is 40ft radius, not an explosion in the centre, and smashes all of each area with bludgeoning directly. And also with heat. I'd argue this makes it more likely that the fire damage happens mostly after the bludgeoning.

So overall this reasoning is inconclusive and wasn't very useful. But at least now we've thought about what happens if we attempt this.

I like my other answer better: neither of them are truly instantaneous and instead both happen over some small interval so one type can heal the other type without having to rule on which happens first.

Answer 5

It doesn't have to be all of one then all of the other

If you model both damage effects as happening over the same fraction of a second: a Golem can take some bludgeoning, absorb some fire, take some more bludgeoning, absorb some more fire, etc.

You can think of both effects as continuous and simultaneous, not actually alternating. (I wouldn't suggest rolling alternating fire / bludgeoning d6s!)

This gives a sensible narrative for subtracting the fire damage from the bludgeoning. D&D is not a physics simulator, but absent other rules some tables may want to go this route if the situation ever comes up.

You don't need to rule on which happens first. There is no truly instantaneous chunk of bludgeoning or fire that all happens before any of the other damage type.