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The War Caster feat (PHB, p. 170) allows a single-target spell ("must target only that creature") to be cast instead of an opportunity attack.

The Green-Flame Blade cantrip (SCAG, p. 142) appears to have a single target, and then some damage "leaps" onto a creature 5 feet away. The other creature is never referred to as the target, or even "a target".

Can the Green-Flame Blade cantrip be cast as a reaction using the War Caster feat?

I'm pretty sure this is solid from the RAW perspective. Is this legit from a RAI perspective?

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The RAI on this one is a little uncertain, from what I can tell.

In this October 2015 tweet, rules designer Jeremy Crawford responded to a question about using the Green-Flame Blade cantrip for an opportunity attack:

Without a feature like the War Caster feat, a spell can never be cast in place of an opportunity attack.

He doesn't make it incredibly clear, but the implication here seems to be that with the feat, this would be possible.

However, this is contradicted by a later tweet in November 2015, in which he stated:

Twinned Spell doesn't work with a spell that targets more than 1 creature. Green-flame blade targets 2.

This explicitly states that the spell targets multiple creatures (and therefore wouldn't qualify for the War Caster benefit), but again in a different context.

My instinct here is to agree with explicit disqualification, rather than implied exception, so I would say the RAI is that you can't use Green-Flame Blade with an opportunity attack.

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    \$\begingroup\$ Wow, JC's comment says Green-flame blade targets 2 creatures, although the spell description doesn't name the second creature as a target, and there's no attack roll or save. \$\endgroup\$
    – Tim Grant
    Mar 27, 2016 at 13:31
  • \$\begingroup\$ This is why it confused me. There are clearly two targets, but one is just circumstantial and it is never treated like most spell "targets". \$\endgroup\$ Mar 28, 2016 at 1:36
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    \$\begingroup\$ Twin spell has an added sentence that makes all the difference in those tweets. "To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level." War Caster has no such sentence. \$\endgroup\$ Mar 2, 2018 at 16:17
  • \$\begingroup\$ He should have said "Twinned Spell doesn't work with a spell that /CAN/ target more than 1 creature. Green-flame blade /CAN/ target 2. Spells cast from War caster themselves inherently /CAN/ target more, you just can't use them to target more when they are casted using war caster. He states that clearly here: "The 3rd benefit of War Caster requires you to target only the moving creature. Eldritch blast works as long as all the beams target it." \$\endgroup\$ Nov 10, 2020 at 11:02
  • \$\begingroup\$ Worth noting that there is a lot of disagreement around what the word target means, for example green flame blame only targets one creature (one attack roll), and just spreads to another, it doesn't actively target them. \$\endgroup\$
    – SeriousBri
    Jan 2, 2021 at 21:56
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Yes, you can, provided you don't hit any other creature with the secondary effect

The third benefit of the War Caster feat says (PHB, p. 170; emphasis mine):

  • When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

As long as the only creature getting hit by the spell is the one that provoked the opportunity attack, it is legal.

In response to a very similar question on Twitter about using eldritch blast (as a character of 5th level or higher) with War Caster, rules designer Jeremy Crawford tweeted the following:

The 3rd benefit of War Caster requires you to target only the moving creature. Eldritch blast works as long as all the beams target it.

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    \$\begingroup\$ A very good point! If Eldritch Blast works, then so too should Green-Flame Blade as long as there is no secondary effect. This does make things a little more context dependent, unfortunately. \$\endgroup\$ Apr 11, 2018 at 21:51
  • \$\begingroup\$ @DerrekBertrand at least you get some extra damage on your OA a better spell might be Booming Blade though. \$\endgroup\$ Apr 14, 2018 at 1:31
  • \$\begingroup\$ As noted in Mekiah's answer, there's an even more relevant set of Crawford tweets (post-2020 errata) about whether green-flame blade (and booming blade) is a valid choice for War Caster's reaction spell. (Also note that Crawford's tweets are no longer considered official rulings, though they might provide insight into the designers' intent in some cases.) You may want to edit your answer to address whether Crawford's unofficial ruling here is supported by the rules. \$\endgroup\$
    – V2Blast
    Feb 24 at 18:33
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This does not work.

As of the November 10th, 2020 errata to the Sword Coast Adventurer's Guide, the green-flame blade cantrip (SCAG, p. 142; TCoE, p. 107) has a range of "Self (5-foot radius)".

However, the third benefit of the War Caster feat says (PHB, p. 170; emphasis mine):

When a hostile creature's movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Since green-flame blade has a range of self, it targets the caster, not "only that creature" which provoked the opportunity attack.


It should be noted that rules designer Jeremy Crawford has stated on Twitter that War Caster still works with green-flame blade. I disagree with this ruling, based on my explanation above, and think he should have made his rules clear enough to not need unofficial rulings on Twitter.

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  • \$\begingroup\$ Relevant question on targeting: What counts as a target for a spell? \$\endgroup\$
    – illustro
    Nov 11, 2020 at 13:51
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    \$\begingroup\$ This seems to be based on a mistaken interpretation of Range vs Targeting. The spell explicitly calls out the target: "On a hit, the target suffers the weapon attack’s normal effects" So if you're the target, you're hitting yourself. \$\endgroup\$
    – G. Moylan
    Jul 27, 2021 at 15:17
  • \$\begingroup\$ You should edit your answer to link to the relevant Crawford tweet(s) – one of which explicitly addresses green-flame blade (not just booming blade). You may also want to elaborate on why you disagree with Crawford's ruling (e.g. by pointing to the rules and explaining how they contradict the ruling). \$\endgroup\$
    – V2Blast
    Feb 24 at 18:17
  • \$\begingroup\$ @V2Blast I disagree with Crawford's ruling because it contradicts the very plain reading of the rules I outlined in this answer. There's nothing more to elaborate on. \$\endgroup\$ Feb 24 at 18:20
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    \$\begingroup\$ Related: Do spells with a range of "Self" target the caster? \$\endgroup\$
    – V2Blast
    Feb 24 at 18:28
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Yes, as long as the fire doesn't "leap" to a second creature

Jeremy Crawford has posted some clarifications regarding spells with a range of "Self" (followed by an area) after the release of Tasha's Cauldron of Everything:

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.

He then posted a followup tweet explicitly stating that the booming blade and green-flame blade cantrips work with War Caster (with a caveat, for the latter):

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.

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This is probably a DM decision. I would say yes as the spell only targets one creature:

you must make a melee attack with a weapon against one creature within the spell's range

The second target isn't directly targeted by the spell, but is hit as an additional property of the spell.

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