Trickery Cleric Invoke Duplicity and BB/GFB interaction

[Biggstick]

I'm not sure if this is possible, so I'm putting it forth to the forums. Could one use the Booming Blade or Green Flame Blade Cantrips with the illusion created by the Trickery Cleric's Invoke Duplicity channel divinity spell? I'll add the RAW for each ability as well in case people are AFB.

Invoke Duplicity: Starting at 2nd level, you can use your Channel Divinity to create an illusory duplicate of yourself. As an action, you create a perfect illusion of yourself that lasts for 1m, or until you lose your concentration (as if you were concentrating on a spell). The illusion appears in an unoccupied space that you can see within 30' of you. As a bonus action on your turn, you can move the illusion up to 30' to a space you can see, but it must remain within 120' of you.
For the duration, you can cast spells as though you were in the illusion's space, but you must use your own senses. Additionally, when both you and your illusion are within 5' of a creature that can see the illusion, you have advantage on attack rolls against that creature, given how distracting the illusion is to the target.

Booming Blade:
Cast time: 1 action
Range: 5'
Components: v, m (a weapon)
Duration: 1 round
As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spells range, otherwise the spell fails. On a hit, the target suffers the attack's normal effects and it becomes sheathed in booming energy until the start of your next turn. If the target willingly moves before then, it immediately takes 1d8 thunder damage, and the spell ends.
Spell damage increases yada dada.....

Green-Flame Blade:
Cast time: 1 action
Range: 5'
Components, v, m (a weapon)
Duration: Instant
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. On a hit, the target suffers the attack's normal effects, and green fire leaps from the target to a different creature of your choice that you can see within 5' of it. The second creature takes fire damage equal to your spellcasting ability modifier.
Spell damage increases yada dada....



I couldn't find a Sage Advice on the subject of this, only on the Spell Sniper/Reach weapon combinations. Any advice or clarification would be fantastic.

[CantigThimble]

I noticed this interaction a while ago. Best I can tell, you could cast the spell on anyone adjacent to the double, but, since the double can't make melee attacks, the spell would have no effect. The only situation where this could work is if you had a polearm and the double was adjacent to an enemy 10 feet away. However, you're probably better off moving into melee range for the advantage in that situation.

[Sander]

"You can cast spells through the double" ... hmm, in other words, a magical conundrum. No, it's actually not an easy question to answer. That being said, I'd say go for it. It says you can cast spells through it - no restrictions - seems logical that the double would then also suffer/gain/perform any actions/bonuses/whatnot stipulated in the spell you cast through it. Also, it might be an illusion, but being a magical effect, I honestly see no reason why it couldn't materialize its weapon or something as part of the spellcasting. This is a fairly expensive combo, considering its merely a neat trick, so I don't see why not. Having said that; Kudos on noticing that interaction, I hadn't considered that before, and that, Sir, is one hella awesome trick!

[MrStabby]

At our table we rules it didn't work (other than as mentioned, using a pole-arm/whip and just using the double to extend range.

To get the effects of the spell you need to hit with a melee attack. If you cant it fails. If the target is too far away you cannot complete that part of the spell. It is a necessary condition.

[Oramac]

the double can't make melee attacks

Invoke Duplicity never actually says the duplicate can't make a melee attack. It just says you can cast spells as if you were in its position.

My interpretation is: go for it!

[CantigThimble]

Invoke Duplicity never actually says the duplicate can't make a melee attack. It just says you can cast spells as if you were in its position.

My interpretation is: go for it!

But it doesn't say it CAN make melee attacks. It also doesn't specifically say the double can't cast wish at will but I'm not allowing that.

[Oramac]

But it doesn't say it CAN make melee attacks. It also doesn't specifically say the double can't cast wish at will but I'm not allowing that.

It says you can cast a spell through the double. Wish is a spell, so if the casting Cleric somehow has access to it, he could cast it through the double (though admittedly there's no real reason to do so).

Also, BB and GFB are spells. Thus they can explicitly be cast through the duplicate.

The question, then, is whether the duplicate can make the requisite melee attack required by those spells. As you say, Invoke Duplicity doesn't say one way or another with regards to melee. Thus, I suppose it would be up to each individual DM to allow or disallow it.

[CantigThimble]

It says you can cast a spell through the double. Wish is a spell, so if the casting Cleric somehow has access to it, he could cast it through the double (though admittedly there's no real reason to do so).

Also, BB and GFB are spells. Thus they can explicitly be cast through the duplicate.

The question, then, is whether the duplicate can make the requisite melee attack required by those spells. As you say, Invoke Duplicity doesn't say one way or another with regards to melee. Thus, I suppose it would be up to each individual DM to allow or disallow it.

My point with the comment about wish wish was to say that the duplicate doesn't have abilities unless the ability specifically says that it does. If invoke duplicity didn't say that you could cast spells as if you were in the duplicate's space then you couldn't. Also, you are the one casting the spell, not the duplicate. The range and direction of the spell changes, but you're still casting it so you need to make the melee attack.