I understand that so long as conditions are met, you can Sneak Attack as part of the melee attack from the Booming Blade cantrip.

Can you dual wield and attack with both weapons after casting Booming Blade? I understand that you probably need something like the War Caster feat and Subtle Spell to pull this off, but I don't know if the melee attack as part of Booming Blade is a bonus action or not.

Can you extend the combo if you had Extra Attack like those from either fighter, ranger, monk, or bard, and use damage-increasing spells like Hex or Hunter's Mark? It's safe to say this build is around Lv 5 or higher.

So is the following combo possible?

  • Build (Human Rogue 4, Ranger 3, Sorcerer 3)
  • 1st Round: Full round act: cast Hunter's Mark and Hex.
  • 2nd Round: cast Booming Blade swing with main hand weapon [weapon + d8 + 2d6 sneak attack]
    then swing again (if with extra attack) [weapon + hunters mark 1d6 + colossus slayer 1d8],
    then swing with off hand [weapon + hunters mark 1d6 + colossus slayer 1d8]

Now if you dip in fighter, can you add Action Surge so you can get two more attacks from your main hand for a possible [2x weapon + hunter's mark 2d6 + colossus slayer 2d8] damage? And 2d8 thunder damage if the targeted enemy goes after the attacker (me)?

No, You cannot combine attacks with booming blade.

Both Booming Blade and Green Flame Blade say the following:

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell's range

This means that these cantrips do not require you to take the Attack action, they require you to take the Cast a Spell action.

If we look at extra attack, it is defined as:

Beginning at 5th level, you can Attack twice, instead of once, whenever you take the Attack action on Your Turn.

No Attack action is taken, so no extra attacks can be used. Additionally, two weapon fighting states:

When you take the Attack action and attack with a light melee weapon that you’re holding in one hand, you can use a bonus action to attack with a different light melee weapon that you’re holding in the other hand.

Again, no attack action is taken, so you cant use a bonus action to make an off hand attack.

In your scenario, you can cast hunter's mark or hex, and then the hit from the booming blade will trigger those effects, as well as sneak attack (if the conditions are met), but you will be unable to make more attacks after that.

Action surge gives you another whole action, which you can use to cast a spell, like Booming Blade which will give you one more attack, or if you just use a regular attack action, extra attack and two weapon fighting could apply.

  • 1
    Not to mention that both hunter's mark and hex require concentration and bonus action to cast. – AntiDrondert Aug 7 at 13:57

That combo will not work, for a number of reasons

First, you cannot cast both Hex and Hunter's Mark. Both require concentration, and both require a Bonus Action to cast, of which you only get one per turn.

Second, and most importantly to the root of your question, casting Booming Blade does not grant any additional attacks, through either the Extra Attack feature, nor Two-weapon Fighting. Both Two-weapon Fighting and Extra attack contain the phrase:

when[ever] you take the Attack action

indicating that they require you to take an entirely different action than the Cast a Spell action that Booming Blade requires.

Third, Colossus Slayer effects only one hit per turn, so you can only add that extra damage once.

Eldritch Knights can almost do this

With seven levels of Fighter (Eldritch Knight), however, you could get close. The Eldritch Knight's seventh level feature grants a Bonus Action attack after casting a cantrip, and the Fighter itself gets the Action Surge feature, which combined would allow to to cast Booming Blade, followed by three (or more, depending on how many levels of Eldritch Knight you take) additional melee weapon attacks, once per short rest.

No, you cannot make an off-hand attack with Booming Blade. Two weapon fighting lets you make an attack with your bonus action when you take the Attack action. Booming Blade is a spell, which requires you to have taken the Cast a Spell action, not the Attack action. It's confusing, because as part of casting the spell you make an attack, but you never made the Attack action, so you never got the chance to use your bonus action to make an off-hand attack.

At 7th level an Eldritch Knight is granted a bonus melee attack following a cantrip based on his/her War Magic feature. If the character casts Booming Blade the cantrip is dependent on a successful melee attack as a part of the spell; here the War Magic feature kicks in and the character may make a second melee attack as a bonus action if he/she has not already taken a bonus action during this same turn.

The above debate comes down to RAW vs. RAI. As the material is written, I believe Reign's interpretation is logical and correct. However, this would seemingly OP characters using these hybrid spell/melee cantrips and stacking Extra Attack and/or a dual wield bonus attack. This seems to break balanced mechanics and is not in keeping with most interpretations of RAI. It would be helpful if WotC would officially rule on this for clarification rather than deferring the matter to individual DM's.

  • 1
    The original querent is inquiring more upon whether or not the they can do what they're proposing. You sort of seem to be answering yes, but then venture towards commentary on what the actual answer is. I recommend editing a bit to make your answer to the asked question a bit more prominent as it's a big ambiguous right now amidst the commentary. – Pyrotechnical Oct 8 at 19:44

As stated in the D&D Player's Handbook, page 194 & 195:

MAKING AN ATTACK
Whether you're striking with a melee weapon, firing a weapon at range, or making an attack roll as part of a spell, an attack has a simple structure.

  1. Choose a target. Pick a target within your attack's range: a creature, an object, or a location.

  2. Determine modifiers. The DM determines whether the target has cover and whether you have advantage ar disadvantage against the target. In addition, spel1s, special abilities. and other effects can apply penalties or bonuses to your attack roll.

  3. Resolve the attack. you make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack.

The last line makes this answer rather easy: if the spell makes you roll an attack roll, it counts as an attack and you CAN combo attacks after it.

  • 3
    For things that trigger on "an attack", they would apply with Booming Blade. However, things related to an "Attack action" would not apply with Booming Blade, because if you use your action to cast Booming Blade, you're using the Cast a Spell action - which is not the same as the Attack action. – V2Blast Mar 1 at 21:27
  • where in the handbook does it say this? "If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll, you're making an attack." speaks in favor of the spell counting as an attack action. – Reign Mar 2 at 8:12
  • Also "ATTACK The most common action to take in combat is the Attack action, whether you are swinging a sword, Iiring an arrow fram a bow, or brawling with your fists. With this action, you make one melee or ranged attack. See the "Making an Attack" section for the rules that govern attacks. Certa in features, such as the Extra Attack feature of the Iighter, allow you to make more than one attack with this action. " This clearly states that for determining when en axtra attack can be made we should refer to the rule I mentioned earlier." – Reign Mar 2 at 8:26
  • The simplest way to put this is : there are 10 different actions: Attack, Cast a Spell, Dash, Disengage, Dodge, Help, Hide, Ready, Search & Use an object. The Added rule 'Making an attack' EXISTS to determine if ur making the First Action. wich is an Attack action instead of one of the other 9 actions and it says : If there's ever any question whether something you're doing counts as an attack, the rule is simple: if you're making an attack roll,you're making an attack. Since there is no other justification to contradict this, a spell for wich u roll an attack roll counts as an attack action. – Reign Mar 2 at 18:13
  • 1
    ...There's a difference between "an attack" and "the Attack action". If you cast a spell (i.e. a spell you know, not via a magic item or something), you're using the Cast a Spell action. Several spells have attack rolls, which means they are indeed "attacks", but that doesn't change the fact that you use the Cast a Spell action to, well, cast the spell. – V2Blast Mar 3 at 3:52

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