September 26, 2022 - 5e, dnd, how-id-rule

How I'd Rule - Booming Blade and Material Costs

Booming Blade was errata'd and it complicates how it works with some weapons, spells. and other gear.

The Tasha's Cauldron of Everything version of Booming Blade:

Casting Time: 1 action
Range: Self (5-foot radius)
Components: S, M (a melee weapon worth at least 1 sp)
Duration: 1 round

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and then becomes sheathed in booming energy until the start of your next turn. If the target willingly moves 5 feet or more before then, the target takes 1d8 thunder damage, and the spell ends.

At Higher Levels. At 5th level, the melee attack deals an extra 1d8 thunder damage to the target on a hit, and the damage the target takes for moving increases to 2d8. Both damage rolls increase by 1d8 at 11th level (2d8 and 3d8) and again at 17th level (3d8 and 4d8).

Throughout this article, Booming Blade and Green-Flame Blade can be used interchangeably for rulings. If the rules allow Booming Blade to work, Green-Flame Blade will work in it's place (and vice-versa). When you see the term "gish" used, it's grouping these two cantrips together as if it were one cantrip/spell.

Rules-as-Written (RAW)

This section is written for Adventurer's League play and for the most rules-driven DMs out there. It's not necessarily how I think it should be ruled or how it would be ruled at most tables -- for that, read the rest of the article.

But let's talk about rule-as-written (and even in this case, rules-as-intended because some of the game designers would rule differently than the errata).

Rules-as-written, the errata has the following impact on the game:

What still works (or works now):

Strictly rules-as-written, a stingy DM won't allow Booming Blade to work with the Artificer's Thunder Gauntlets because there's no written/established value set for Thunder Gauntlets in the rules. Ideally, you'd see something mentioning the value of these gauntlets in the sourcebook. That said, strictly rules-as-written magic items do not have a value. They cannot be bought or sold so there is no established price in the rules and technically can't be used as a material component for the spell.

The Intent of the Errata

If a D&D spell’s material component lacks a monetary value and isn’t consumed, you don’t need that component; you could substitute a component pouch, for instance.

Booming/Green-Flame Blade need a weapon with a monetary value because they require an actual weapon. #DnD

- Jeremy Crawford (@JeremyECrawford)

This explanation doesn't make sense to me because you'd still need to make an attack with a component pouch and no rules handle that well. Also, from an optimization point of view, the component pouch would be improvised and use the creature's strength modifier -- so a STR attack with no proficiency bonus and most classes interested in a component pouch use STR as a dump stat.

I guess from a rules perspective, the melee attack was ambiguous -- are you making the attack with the physical weapon or are you making a spell attack that acts like a weapon (using your spell attack modifier instead). It was always clear to me the intent was to use a weapon to make the attack and the errata makes it clear(er) that it's a weapon attack and not a spell attack so it's hard for me to believe the explanation above; it sounds like there was a disagreement about the intent/power level of the cantrip and maybe not everyone in the room agreed with the changes.

Making this even more confusing from a rules perspective, Jeremy Crawford specifically said he'd allow Shadow Blade (and other improvised weapons) work even after the errata:

This change has nothing to do with prohibiting or allowing Shadow Blade to combine with Booming/Green-Flame Blade. It's about fixing those two cantrips. As DM, I'd allow those them to combo, since I make liberal use of the rule on improvised weapons.

- Jeremy Crawford (@JeremyECrawford)

And that Booming Blade should work with War Caster:

The Booming Blade spell continues to work with the War Caster feat. The spell targets one creature.

The Green-Flame Blade spell continues to work with War Caster if you forgo targeting a second creature with the green fire. #DnD

- Jeremy Crawford (@JeremyECrawford)

The interesting part of this tweet is the implication that you can chose to forgo the targeting of a second creature -- and since the secondary effect of Green-Flame Blade does not target, it should still be valid (this rationale comes from Magic the Gathering rules regarding targeting vs choosing but it seems like a relevant explanation for this situation).

A note about D&D spells with a range of "Self (XYZ)": the parenthetical—which says "5-foot radius," "15-foot cone," or something else—means you are the spell's point of origin, but you aren't necessarily its target. You're creating an effect that originates in your space. #DnD

- Jeremy Crawford (@JeremyECrawford)

Note: The date of these two tweets are November 11th, 2020. Tasha's Cauldron of Everything was released on November 18th but I believe the errata for Sword's Coast came out on the 11th.

How I'd Rule This

In general, Booming Blade is vastly overrated. It keeps up in damage with multiattack before other buffs are taken into account and it's most useful when it stacks with a Rogue's Sneak Attack (and this is where it really shines because Rogues don't get multiattack). Stacking effects on top of Booming Blade doesn't feel good when you're a new DM but it's not going to be a huge increase in damage or utility by allowing it. Monks with Disengage, a Swashbuckler Rogue stepping away, or a player character with the Mobile feat will have an easier time triggering Booming Blade than letting an Artificer stack a debuff with Booming Blade.

Does Booming Blade and/or Green-Flame Blade work with the Artificer's Thunder Gauntlets?

For me, the gloves/gauntlets are part of your armor and your armor is worth some value. So I'd allow it.

To expand on this a bit, you typically can't buy gauntlets only when buying armor; the gauntlets are part of your power armor (and your power armor is heavy armor os some sort that has a value specified in the PHB/DMG).

Note: This might sound absurd, but it came up on Reddit. Just because armor grants +1 to AC, it does not also increase the attack modifier or damage of the Thunder Gauntlets. This is a bad faith argument.

Should Booming Blade work with Shadow Blade, Spiritual Weapon, or other conjured/improvised/natural weapons?

This question requires three different answers.

The Good: For me, Shadow Blade works the same way Thunder Gauntlets does but has a slightly different rationale. Shadow Blade requires resources to be spend (and uses Concentration) so the game partially balances for this already -- and since the intent of the errata was to clarify that Booming Blade requires an attack with a weapon (not a Component Pouch), Shadow Blade can be used in good faith. For the sake of the argument, I'd consider the blade conjured by Shadow Blade to be worth the value of a dagger, shortsword, or scimitar (they wouldn't be allowed to sell it because people would recognize common illusion magic and know it will disappear).

The Bad: Spiritual Weapon is a hard no for me. The argument could be made that because Spiritual Weapon makes a weapon attack that casting Booming Blade could use Spiritual Weapon as the weapon (especially with the old version of Booming Blade) but this argument is nonsensical to me -- to use Booming Blade the character must make the attack, not some other entity (for other reasons, a familiar cannot make an attack with Booming Blade but similar logic should apply here).

The Ugly: Improvised weapons (and natural weapons) get a pass for me, they should work with Booming Blade and Green-Flame Blade. And even though this question doesn't ask about Unarmed Strikes -- Unarmed Strikes go against the intent of Booming Blade.

Conjured items, specifically through the Wizard's Minor Conjuration feature or Bard's Performance of Creation, I'd cautiously allow it because things that don't have a damage value assigned to it generally shouldn't do damage. Again, we're looking at intent here (and the resource cost comes into play). If the player is looking to abuse the situation, then rule against it (see Purple Wurm Poison) but for the most part, if I'm allowing Shadow Blade to work because it has a damage property assigned to it and a player says they want to conjure a Dagger, the dagger should operate in the same way a normal dagger works.

Natural weapons get punished by not being weapons and I'd generally rule that any time something needs a weapon, natural weapons should apply (I reserve my right to change my judgement but this shouldn't break anything) -- plus, most natural weapons have an implicit value to them (for example, one could reasonably expect to sell minotaur horns). Unarmed Strikes work slightly different and it's more clear with the One DND rules, that were previewed in August of 2022, that an Unarmed Strike is treated as a different type of attack. Another Jeremy Crawford tweet (but from much earlier):

As DM, I'd allow a natural weapon (not a regular unarmed strike) to work with an effect like booming blade. #DnD

- Jeremy Crawford (@JeremyECrawford)

Does Green-Flame Blade work as an Opportunity Attack with War Caster?

Yes, but I'm going against the game designers here. Green-Flame Blade and War Caster came up in a Jeremy Crawford tweet earlier in the article but I wanted to make it clear how I'd rule it here. Green-Flame Blade only targets one creature with a range, so I'd allow it to be used with War Caster's opportunity attack. The secondary damage applies to a creature within range of the first but it doesn't specifically target that creature.

It's a little rules-lawyerly on both sides but the player invested in War Caster and if they wanted to use Green-Flame Blade in a situation where they know Booming Blade's damage would trigger, there's probably a good reason for doing so (plus, they took both cantrips... there's a cost associated with that as well).

Further Reading