How does a Web holding large creatures behave when set on fire?

Question

The final two sentences of the Web spell are written as follows:

The webs are flammable. Any 5-foot cube of webs exposed to fire burns away in 1 round, dealing 2d4 fire damage to any creature that starts its turn in the fire.

Does this mean that a creature in multiple Webbed squares takes 2d4 damage per flaming Web square, or just a flat 2d4?

This question arose recently as a debate in my game recently, centering around the word "any" at the start of the last sentence.

We were facing a gargantuan creature, and some of the players at the table, having read the last couple sentences, convinced the DM that since the spell said "any" 5ft cube exposed to fire, and with the casting of a fireball immediately after casting the web (second PC), ALL of the adjacent/occupied cubes of the web spell would ignite simultaneously, then each square occupied by the gargantuan creature (20ft base, matching the 20ft base of the web) would deliver 2d4 fire damage as it burned away in that first round.

At the time, the DM ruled this correct and subtracted 1/3 of the total cubes to account for the volume of the creature within the web (I would have subtracted 3/4 of the cubes at least for this - if this were the correct ruling to begin with).

This resulted in 64 cubes (the number of 5ft cubes in the 20x20x20 area of the web) minus 22 cubes (roughly 1/3 of that, rounded up) - total of 42 cubes each causing 2d4 fiber damage as it burned in one round. 84d4 fire damage. It added up to about 200 HP in fire damage.

I am thinking that it's likely the intent of this rule is that the TOTAL damage experienced by any ONE creature within a web spell effect suddenly ignited is - 2d4 fire damage.

RAW though - the English major within me can't shake that is says "Any", and the fire noted at the end of the sentence is referring to the fire of "any" specific 5ft cube, not the entire web, and a fireball would ignite all of them at once.

What is the correct interpretation of this spell, and how do you justify your answer?

"Because it is ridiculous to assume anything else," would not be a valid answer.

I have sent a tweet to Jeremy Crawford for an answer as well - but haven't received a response.

Finally - why do I need this? I'll be DMing this same group starting in a week and a half. I won't be allowing them to wipe legendary creatures in two rounds with this technique regardless - but I want justification on hand to shut them down when I say "no". I know, as a DM, I can do that anyway, but this is a game at my LGCS and I really want to keep things as peaceful as possible.

Answer 1

The webs are flammable. Any 5-foot cube of webs exposed to fire burns away in 1 round, dealing 2d4 fire damage to any creature that starts its turn in the fire.

As I read this: "Any" indicates that individual cubes can be affected (rather than the whole web). However "the fire" indicates that there is still just one web-fire each round, and a creature is either in it, or is not (i.e. a binary condition). This is consistent with other D&D paradigms in that larger sized creatures do not take more damage from area or environmental effects.

fwiw: (since the 5e writers purposefully used earlier editions for inspiration), the 3.5e text for web said "Any fire can set the webs alight and burn away 5 square feet in 1 round. All creatures within flaming webs take 2d4 points of fire damage from the flames.". It seems like the intent here too was to have individual sections be burnable, but not to have variable (size dependent) damage.

Now I personally might still allow a PC to stretch out the damage by say, burning just one cube each round (which might seem counter-intuitive to the above ruling, but is as least balanced and consistent with other D&D paradigms).

Answer 2

No.

The intent is that one action = one saving throw and one instance of damage.

Justification: If a large creature (four 5' squares) starts its turn in the area of effect of a spirit guardians spell, it takes damage once, not four times. The same applies to blade barrier, fireball, burning hands and so on.

So, in the scenario above, I would rule that one fireball means the large creature makes one saving throw against the burning webs and takes one instance of damage (with a second for the direct effects of the fireball, of course).

It would play like this:

1. Player's turn: Character casts fireball. The GM rolls a saving throw, the monster takes damage from the fireball. The entire webs is set alight.
2. Monster's turn: The monster starts its turn in the burning webs (since it hasn't had a chance to move away). The GM rolls a saving throw, the monster takes 2d4 damage (depending on the roll).
3. Player's Next Turn: At the start of this turn, the burning webs go out.

Answer 3

The Creature Only Occupies Its Size, Not Its Space

Player's Handbook, Space section, p191

A creature’s space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn’t 5 feet wide, for example, but it does control a space that wide...

Physical dimensions are what's important here. The creature's actual volume, in 5' cubes is how many cubes-worth of damage it risks from the webs (PHB, p287-8) burning, not its space.

A medium or smaller creature is always 1 5' cube in volume (the smallest 'resolution' that the web spell dictates). A large creature is likely 2 cubes; an ogre being about 10' tall and 5' wide, a horse about 5' tall and 7' long. A huge creature might be about 4-8 cubes (fire giant, adult dragon). And a gargantuan creature might be about 10-24 cubes, or more.

Result!

Presume that the creature is in the worst possible situation; it's moved all the way into an existing web in a 20' by 20' hallway (webs on open ground are only up to 20' by 20' by 5' tall, as the spell says).

The medium or smaller creatures take 2d4 damage (5 avg), a large creature takes 4d4 (10 avg), a huge creature takes 8-16d4 (20-40 avg), and the gargantuan creature takes 20-48d4 (50-120 avg).

Conclusion

Yes, I'm saying that the web spell can cause a creature larger than medium more damage, due to its wording. This damage potential is mitigated by taking more actions, and requiring 'perfect' circumstances.

The only thing I see wrong with the earlier DM's ruling is being on the wrong side in space vs size.

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Cover rules in regards to spellcasting mean that if casting web on a space already occupied, there's a 'shadow' from the origin to the opposite side of a creature. So it's very hard to surround a creature in a web unless it tries to move through an existing web.