Armorer Artificer Off-Hand with Power Armor?

Question

OK, so the armorer artificer (UA) specialization states:

Lightning Launcher. A gemlike node appears on one of your armored fists or on the chest (your choice). It counts as a simple ranged weapon, with a normal range of 90 feet and a long range of 300 feet, and it deals 1d6 lightning damage on a hit. Once on each of your turns when you hit a creature with it, you can deal an extra 1d6 lightning damage to that target.

Page 195 of the PHB states:

TWO-WEAPON FIGHTING
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. You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative. If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.

(emphasis mine)

This, to me, implies that the artificer can use a shield, have his gem-node on his chest attack, and still has a hand free for an off-hand thrown weapon attack (as long as it's a simple weapon). The fact that one of his infusions can allow boomeranging thrown weapons make this viable if, you know, it's viable.

Anyone have any insight?

Answer 1

Lightning Launcher cannot be used with two-weapon fighting

The requirement to use two-weapon fighting is to be holding 2 light melee weapons, one in each hand. The Lightning Launcher is neither light, nor a melee weapon, nor handheld, so it does not qualify for two-weapon fighting.

You can still attack with the launcher and another weapon with Extra Attack

However, as a Armorer of 5th level or higher, you have Extra Attack, and there's nothing to stop you from using your 2 attacks to attack with 2 different weapons. So in the situation you describe, where the armorer wields a shield in one hand and a weapon in the other, and also has the lightning launcher equipped, they could make one attack with the lightning launcher and the other with the weapon in their hand, all while keeping their shield equipped.

(Of course, you can also just attack twice with the launcher, or with your held weapon.)

Answer 2

This doesn't work as the Lightning Launcher isn't a light melee weapon held in one hand

In your Two Weapon Fighting quote, it specifically says that you need to be holding two weapons in each hand:

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.

Since one of the weapons in your case is mounted on your chest, this isn't in your hand, and therefore doesn't count towards Two Weapon Fighting. This is shown by the bold emphasis in the above quote.

Besides that detail, the chest mounted weapon is also an invalid weapon for use with Two Weapon Fighting for the same reason that a sling wouldn't be valid; it is a simple ranged weapon, but not a light, melee weapon. This is shown in the italics emphasis in the above quote.