Does the Draconic Bloodline sorcerer's Elemental Affinity feature apply to the spell Dragon's Breath?

Question

The Draconic Bloodline sorcerer feature Elemental Affinity states:

[When] you cast a spell that deals damage of the type associated with your draconic ancestry, you can add your Charisma modifier to one damage roll of that spell.

The dragon's breath spell (XGtE, p. 154) incorporates a damage roll, but it is not a direct consequence of the spell:

Until the spell ends, the creature can use an action to exhale energy of the chosen type in a 15-foot cone. Each creature in that area must make a Dexterity saving throw, taking 3d6 damage of the chosen type on a failed save, or half as much damage on a successful one.

Would one of these exhalations qualify for the application of the Elemental Affinity feature? If so, is only one eligible or every one throughout the duration of dragon's breath

Answer 1

You can use it. Once.

It's a spell, and it does deal damage of the chosen type (assuming you choose the same type for the dragon's breath as you have for your bloodline). That meets the requirements for applying the class feature to that casting of the spell. The spell likewise has associated damage rolls, and thus the bonus can be applied. There is no listed requirement that anything be a "direct consequence" of anything. It's just as applicable here as it would be with wall of fire or produce flame - each of which applies damage at times and based on triggers other than the instant of the casting.

This, as stated in the class feature, allows you to add your charisma modifier to one damage roll of the spell - in this case one exhalation. Any other exhalation would be a different damage roll, and wouldn't get the benefit. Timing here could get kind of odd, amusingly, as it never tells you you have to add it to the first damage roll of the spell, and it doesn't tell you if you decide whether or to add it before or after you roll the dice, but the "Yes it works, use it once." part is pretty clear.

The "one damage roll per spell" is accurate, though was not in the original printing. It's an errata.

Per The Player's Handbook Errata,

Elemental Affinity (p. 102). The damage bonus applies to one damage roll of a spell, not multiple rolls.

Answer 2

It does not apply, the damage is caused by spending an action - not casting a spell.

As quoted above, Elemental Affinity engages when(emphasis mine):

you cast a spell that deals damage of the type associated with your draconic ancestry...

When you cast dragon's breath, you are not dealing damage. You are granting an ability for whomever it is cast on to(emphasis mine):

use an action to exhale energy of the chosen type in a 15-foot cone.

It is when you use that action, not when you cast the spell, that is dealing the damage.

You are using your action to utilize the effect granted by the spell, but not spell is being cast. The spell is only giving the creature the ability exhale energy.

**You are not meeting the requirement of casting a spell when you are dealing the damage and therefore can not use your Elemental Affinity.

The damage dealing effect is similar to Breath Weapon of a dragonborn.

There is no spell being cast, it is just an ability that uses an action to engage. When you deal the damage, you are expending an action. Granted, it's an action given to you from a spell, but the damage is dealt from the action - not from casting a spell.

The fact that a spell gave you that ability doesn't change the mechanic of its use. When you're dealing the damage, it is not from casting the spell. It is from using the action granted by the spell (which, again, is not casting a spell.)

Strict vs loose reading

Ultimately, I think there is some ambiguity and it depends entirely on how you read the spell. Given that we are talking about a feat here and one concentration-based spell, I don't think it'd be a huge deal to grant it by stating that the spell is ultimately causing the damage on one breath attack action during the spell duration.

This is somewhat supported by the same initial line. The difference is in granting

cast a spell that deals damage...

to the end-action for the damaging effect and not just the spell itself.

If it becomes overused, then you can always go back to the stricter after discussing it with your player.

But the hard line reading does suggest that this interaction doesn't work given you aren't casting a spell to cause the damage.