D&D 5E Invoke Duplicity + Booming Blade + Sneak Attack

[TrueBagelMan]

So if a Rogue/ Trickery Cleric used invoke Duplicity and cast booming blade through it could it deal sneak attack damage? I’m not sure if I’m rules lawyering or not, but would this work? The second question is do you deal damage the sword would make with booming blade? Is booming blade a viable spell for this?

 

[Paul Farquhar]

I assume the cleric is equipped with an eligible weapon and getting sneak attack from multiclass?

In this case, the rules are unclear.

The illusory duplicate doesn't have a real weapon it can attack with, so I would probably rule that you could only use this trick if the cleric is also close enough to attack the target with their weapon. I.e. the spell originates from the illusion but the weapon attack actually originates from the cleric (but appears to originate from the illusion). This would be most useful if a whip is the weapon in question.

 

[Benjamin Olson]

"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, otherwise the spell fails."

You've got to make a melee attack on the creature. YOU must make an attack. Your duplicate isn't you, and does not allow you to make melee attacks from its position, only cast spells as though you were there.

Invoke Duplicity arguably could be used to determine range enabling you to make the melee attack with a reach weapon from 10 feet if your duplicate stood next to them (whip might be cool for the Rogue, but you miss out on the advantage from both standing next to the enemy).

Since you are a Rogue I would just be thankful for having a special duplicate buddy to give you melee advantage all the time and boom your blade the normal way.

 

[Paul Farquhar]

^^This is my interpretation as well, although, to play devil's advocate, it doesn't say you must be able to make a melee attack against the target (badly worded spell is badly worded), and the word "you" in spell descriptions can also refer to the origin point of the spell - e.g. Shocking Grasp familiar.

An alterative, less RAW take, could be that the illusion makes a melee attack with an illusionary weapon, which does zero damage but can apply the Booming Blade effect.

 

[DND_Reborn]

For casting booming blade through the duplicate, I would say not. This is because the duplicate cannot make a melee weapon attack, which is a requirement for the booming blade spell.

Since the illusion can grant you advantage in combat, that would allow the rogue part of your PC to employ sneak attack if you cast booming blade yourself, of course.