Are dice re-rolled together or sequentially for Chaos Bolt with the Metamagic option Empowered Spell?

Question

The Sorcerer's Empowered Spell metamagic option reads

When you roll damage for a spell, you can spend 1 sorcery point to reroll a number of the damage dice up to your Charisma modifier (minimum of one). You must use the new rolls.

While the spell chaos bolt reads:

You hurl an undulating, warbling mass of chaotic energy at one creature in range. Make a ranged spell attack against the target. On a hit, the target takes 2d8 + 1d6 damage. [...] If you roll the same number on both d8s, the chaotic energy leaps from the target to a different creature of your choice within 30 feet of it. Make a new attack roll against the new target, and make a new damage roll, which could cause the chaotic energy to leap again.

If Sorcerer chooses to use Empowered Spell when they cast chaos bolt (and has a Charisma modifier of at least +2), do they need to re-roll all of the dice that they wish to re-roll at once? Or can they re-roll one d8, then, if it does not match, re-roll the other?

As an example:
The sorcerer casts chaos bolt and rolls a 7 and an 8. They use Empowered Spell, and re-roll the 7, getting a 3.

If Empowered Spell dice rolls are sequential:
The sorcerer casts chaos bolt and rolls a 7 and an 8. They use Empowered spell and re-roll the 7 getting a 3. The sorcerer uses the additional re-roll allowed by empowered spell to re-roll the 8 and gets a 3 causing the spell to jump to another target

If Empowered Spell dice rolls are rolled together:
The sorcerer already chose to just re-roll the 7 and so cannot now choose to re-roll the 8. The spell does not target another creature.

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A related unofficial tweet from December 2017 by Jeremy Crawford on the subject:

When casting Chaos Bolt and using the Empowered Spell metamagic on the first damage roll, would you be able to reroll only up to the first two d8s, or would you be able to reroll potential secondary damage dice too assuming your charisma modifier was high enough?

You can reroll as many dice as your Charisma modifier allows.

A related question: Which yields higher average damage, an Empowered or Twinned Chaos Bolt?

Answer 1

It depends what books you are playing with

If you play without Xanathar's Guide to Everything, there are no explicit rules regarding simultaneous event resolution, so there's no particular guidance here except as regards game balance considerations (rerolling sequentially isn't a problem; empower is a relatively weak metamagic) and that whatever the DM decides goes.

If you play with Xanathar's Guide to Everything, then the following rule applies:

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.

Rolling a die is a thing that happens. When you roll 2d6 damage, two die are being rolled at the same time. When you choose to reroll a die, that's also happening "when you roll damage", which is the same time. Thus the participant who controls the entity whose turn it is, which is usually the caster, decides what order the rerolls and original rolls which are theoretically all happening and being decided on at the same time actually happen in.

Answer 2

The Metamagic option Empowered Spell says it may be used "when you roll damage for a spell."

When you rolled all three of the dice, you were rolling damage for the spell. Your decision of how many and which dice to re-roll (one, or up to your Cha limit, two; a d8 or the d6) needs to be made at that time (after you see the results of the initial roll). So long as nothing else has happened, you are still in that "when you" moment.

A subsequent event, like re-rolling of one of the damage dice, means that you have moved forward in time; it is no longer the moment when you rolled damage for a spell. The XGtE optional rule on timing does not come in to play, because 'two or more things' are not 'happening at the same time'. 'When you roll for damage' is one time, at which point you declare your use of the metamagic and decide which dice to reroll. Actually making those re-rolls is a later point in time.

Put another way, Empowered Spell has a certain trigger to take effect - at that time, you decide what the effects of it are. If you have moved on and are already resolving its effects, you must have passed the point of the trigger and are beyond your window of decision-making.

Answer 3

To give an interpretation with my DM hat on:

The wording of the ability is "reroll a number of the damage dice". To me that is one reroll, of a number of dice. So when you activate the ability, you pick "a number of the damage dice" and reroll them.

In your 'sequential' example, you can make one reroll then decide whether to make another. That is clearly multiple rerolls (as you say in the example, "the additional reroll") so I would not allow it at my table, and I suspect it's not what the designers intended (although you'd need word of God to confirm).

I don't really see a logical interpretation of the wording that would allow the 'sequential' example you give above.

Answer 4

When you roll damage for a spell, you can spend 1 sorcery point to reroll a number of the damage dice up to your Charisma modifier

When you spend the sorcery point, you can reroll a number of damage dice.

You can reroll 1 die, because 1 is a number.

You can reroll 2 dice, because 2 is a number.

You cannot defer the decision of how many dice to reroll until after you have seen the results of previous dice, because "maybe 1 and maybe 2, I don't know yet" is not a number.

Answer 5

Frame Challenge: It doesn't matter whether you reroll the damage dice, you can't make the spell leap

The d8's used are serving many functions. They are damage dice, to be sure, but they are also determining what kind of damage the spell does and whether or not it leaps to another target.

Empowered Magic lets you reroll the damage aspect of a die or dice, but does not alter their original value for their other aspects. Conceptually, it takes what was one die representing three different things and separates it into different dice, all reading the same roll. Then it lets you reroll the die representing damage, but not the other aspects.

This interpretation does not address your specific question about whether the dice may be rolled sequentially, but it makes the question itself moot if your goal was not to change the damage rolls but to try to generate a leap.

Indirect support for this interpretation can be found at How does an Evocation wizard's Overchannel feature interact with the Chaos Bolt spell? with both GreySage's well-received answer and Xirema's as well. Overchannel does not let you reroll the dice of Chaos Bolt, but rather sets damage to the maximum. In doing so, however, GreySage argues that changing the damage aspect of the dice does not alter their other aspects - just because the damage is now 22 (8+8+6), does not make the Chaos Bolt leaping thunder damage. While not directly analogous to the situation with Empowered Spell's actual rerolls of physical dice, I believe its distinction of the different functions of the dice (damage amount, damage type, ability to leap), supports this answer's interpretation of the question at hand.

Answer 6

Are you rolling damage? Is it for a spell?

If the answers are “yes” and “yes”, you can spend 1 point and reroll up to CHA mod dice.

Each time you roll damage for Chaos Bolt the answers are “yes” and “yes” so you can [see above]. However, due to the restriction that only one Metamagic option can be used on any one spell, you can only do it once.