Questions regarding using a 'Booming Shadow Blade' and multiple attacks per turn...

[samcifer]

So I tried out the SB = BB combo back in November and again during what turned out to be the final session of our campaign last night, but people have mentioned extra attacks with the combo and wonder how it actually works. I was also twinning BB (was playing a sorcadin), so I wasn't sure if that meant I got to attack 2 times in a row with it (the DM let me do so). So how does it work, exactly? I want to make sure I know the proper rules on this but haven't found any regarding twinning and/or extra attack.

[Man_Over_Game]

So I tried out the SB = BB combo back in November and again during what turned out to be the final session of our campaign last night, but people have mentioned extra attacks with the combo and wonder how it actually works. I was also twinning BB (was playing a sorcadin), so I wasn't sure if that meant I got to attack 2 times in a row with it (the DM let me do so). So how does it work, exactly? I want to make sure I know the proper rules on this but haven't found any regarding twinning and/or extra attack.

Officially, Casting a Spell and Attacking both require an Action. Attacking just has you make a basic attack with whatever weapon you're using, up to the number of times you can normally attack (including things like Extra Attack).

Casting a Spell has you follow all the normal rules for casting that particular spell. Spells like Booming Blade have you make an attack as part of casting the spell, just like how spells like Flaming Sphere let you move the Sphere as a Bonus Action.

This means you cannot do the Cast a Spell and the Attack Actions with the same Action. This also means that things like Booming Blade have their own attack that they tack on, ignoring anything regarding Extra Attack or the Attack Action.


However, Twin Spells does let you double a spell onto two targets, so you'd be able to cast Booming Blade on two targets at the same time. Since the spell causes you to attack the creature(s) you target with it, you attack both creatures at the same time. This still has nothing to do with the Attack action or Extra Attacks.

TLDR: Booming Blade is a special spell that makes you attack. This is different from the Attack Action, and only the Attack Action lets you use Extra Attacks.

[Chronos]

The Extra Attack ability, like fighters and barbarians get, only matters when you're using the Attack action. Booming Blade is the Cast A Spell action, and so Extra Attack is completely irrelevant.

Metamagic is relevant to casting a spell. So you could cast Twinned Booming Blade, as long as you can attack two different targets, and deal weapon damage plus booming to both of them.

[RogueJK]

An Eldritch Knight character could also use his class feature War Magic to allow them to Cast a Cantrip (Booming Blade) and then get a Bonus Attack, while holding and concentrating on a Shadow Blade.

This would allow them to make a Booming Blade Shadow Blade attack + a Bonus Action Shadow Blade attack, all in one turn.


Or if the Eldritch Knight used his Action Surge class feature too, they could Booming Blade Shadow Blade attack + Bonus Action Shadow Blade attack + Action Surge Shadow Blade attack, all in one turn.

[sithlordnergal]

As others mentioned, you cannot make an Extra Attack with Booming Blade, or Green Flame Blade for that matter. However you can Twin Spell Booming Blade to cast it twice and attack twice. You can also Quicken Spell both Booming and Green Flame Blade. It costs one more Sorcery Point, but you can target the same creature twice.

[Willie the Duck]

However, a sorcadin (of paladin level 5+) could attack twice with the shadow blade, utilizing the extra attack feature on the non-spell normal attack action (simply with a weapon created by a spell) and then do a quickened Booming Blade with the shadow blade as a bonus action (so not on the round you cast Shadow Blade).