How much damage does a creature take for spending its entire turn inside a Wall of Fire?

Question

The conditions for when wall of fire deals damage, after the initial casting, are as follows (emphasis mine):

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

This is a bit confusing, because it seems like there might be two separate effects that can each deal damage to a creature that ends its turn inside the wall itself. Specifically, if the creature starts its turn inside the wall and remains in the wall for its entire turn, it looks like both effects would trigger at the end of its turn, dealing a total of 10d8 fire damage. (It also looks like a creature that enters the wall on its turn and remains there might take 10d8 total, but not all at the same time.)

Is this intended to deal double damage to a creature that spends its entire turn in the wall, or is the wording simply a bit redundant? How much damage does a creature take if it spends its entire turn inside the wall of fire?

Answer 1

It takes 5d8 damage total.

On its turn in initiative, a creature starting its turn in the wall does not take damage. Doing actions in it does not cause the creature to take damage. Ending its turn in the wall deals 5d8 damage.

Therefore, 5d8 damage is dealt to a creature that spends its entire turn in the Wall of Fire.

The sentence structure of the spell - two separate sentences saying that a creature ending its turn in the wall takes the same 5d8 damage - is redundant. Otherwise the spell would be re-written as, "A creature entering the wall takes 5d8 damage. A creature ending its turn in the wall takes 10d8 damage."

Answer 2

There's a few spells with wording like this; Moonbeam has some janky stuff like that as well. If you logic it out, it's actually specifically designed to prevent a creature from taking damage from that source more than once in a round - in Moonbeam's case because that spell lets you move the beam over an enemy, in both spells' cases because someone might throw a creature into the effect while it's not the creature's turn.

The "On a creature that ends its turn" bit really ought to come after the "...enters the wall for the first time on a turn..." bit, because it's that second bit that gives the relevant information. It's the "OR" that's important here, because without that, you'd get exactly the situation you describe. But with the Or, it becomes:

if (creatureInRangeEndofTurn=True)||(creatureInRangeMoved=True)
     Damage=5d8
;
return 0;

Instead of:

if (creatureInRangeEndofTurn=True)
     Damage=5d8
;

if (creatureInRangeMoved=True)
     Damage=5d8
;
return 0;

The first bit is really the redundant part.

Answer 3

There's several different ways this can play out. I've drawn the following diagram to help make sense of this:

• A: The "Safe" side of the wall; no one takes damage here
• B: The Wall itself, 1' thick.
• C: The 10' field in "front" of the wall
• D: Beyond the limits of the wall; no one takes damage here

Based on how a character acts, they might or might not take a certain amount of damage.

Character at B when wall appears: 5d8 (DEX Save for Half) during the caster's turn

When the wall appears, each creature within its area must make a Dexterity saving throw. On a failed save, a creature takes 5d8 fire damage, or half as much damage on a successful save.

—Wall of Fire, Player's Handbook, pg. 285

Character stands in B through the entire duration of their turn: 5d8+5d8 at the end of their turn

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

—Wall of Fire, Player's Handbook, pg. 285

This needs to be closely examined. Per the RAW, the damage is listed twice. So this damage must occur twice. This might be an oversight/mistake in the spell description, but that is what it says it does.

As DM, I'd probably only use one source of fire damage at the end of the turn, given that I very strongly believe that this is a mistake/not the Rules as Intended. But that would not be a Rules-as-Written ruling.

Character moves from A to B: 5d8 when they enter, 5d8+5d8 when their turn ends

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

—Wall of Fire, Player's Handbook, pg. 285

As established previously, stopping the turn at B results in two sources of 5d8 damage. The only thing new is the additional damage from entering the wall.

Character moves from B to C: 5d8 damage when their turn ends

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

—Wall of Fire, Player's Handbook, pg. 285

Character moves from A to C: 5d8 damage when they enter the wall, 5d8 when their turn ends

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

—Wall of Fire, Player's Handbook, pg. 285

Character moves from A to D: 5d8 damage when they enter the wall

One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.

—Wall of Fire, Player's Handbook, pg. 285

Character moves from B to D: no damage

You didn't "enter" B, and there's no damage for "Entering" C, so ultimately, no damage is issued.

Character moves from C to B: 5d8 damage from entering the wall, 5d8 at the end of turn

Same as moving from A to B.

Other combinations

As far as I can tell, there's nothing surprising in any other set of movements. The rules for "entering" a zone only apply to B, and the direction otherwise doesn't matter. The rules for "ending turn" in a zone apply to both B and C, with slightly variant rules; but the order of entry doesn't matter for those rules.

Answer 4

By RAW, 15d6

One side of the wall [...] deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side [...].

The inside of the wall is withing 10 feet of the side, so this part of the spell does 5d8 damage. Additionally,

One side of the wall [...] deals 5d8 fire damage to each creature that ends its turn [...] inside the wall.

Since that condition is satisfied, that's an extra 5d8 damage.

A creature takes the same damage when [...] it ends its turn [in the wall].

Same damage means 5d8. And 5d8 + 5d8 + 5d8 = 16d8.