Bonus action attack ability score modifier

Question

This may be confusing but currently in the campaign there is a warlock with a magic revolver that allows them to add eldritch invocations related to eldritch blast to the weapon. So agonizing blast adds damage to the weapon. Question:
If this weapon was to be used for a secondary attack, such that You do not add your ability score modifier to the damage of these attacks, unless that modifier is negative, (like general two weapon fighting rules) would this remove the bonus damage of only the ability score modifier used to fire the gun, or, would it remove both that and agonizing blast?

Answer 1

You can't use the revolver at all as a secondary attack with two-weapon fighting rules, as they state

you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand.

So unless you are punching the enemy with the revolver, you can't use it as a secondary attack.

Possibly you could let the revolver count as a hand crossbow for the "Crossbow Expert" feat, and get a secondary attack from that, but then the secondary attack is not due to two-weapon fighting and would therefore gain the ability score modifier added to damage in the usual way.

Answer 2

As it stands, the wording is pretty clear:

You do not add your ability score modifier to the damage of these attacks, unless that modifier is negative.

Normally only one modifier is being added (STR, DEX mainly) but in this case it is two, whatever modifier is used with the weapon and the CHA of the Warlock.

But the rule says you don't add the modifiers, end of story RAW.

However, this is clearly a homebrewed effect so your DM will have to make a decision.

Answer 3

You can add your Charisma modifier

Assuming your homebrew rules allow you to make a bonus action ranged weapon attack with your revolver and assuming this attack follows the same rules as Two Weapon Fighting regarding adding your ability modifier to damage then Agonizing Blast would grant a bonus to the damage of your bonus action attack.

The rules for Two Weapon Fighting state:

You do not add your ability score modifier to the damage of these attacks, unless that modifier is negative.

The issue is that they don't themselves indicate what they mean by "your ability score modifier". You have more than one ability score and the rule doesn't say "any of your ability score modifiers".

If someone says "I won't go to your performance" that is very different from "I won't go to any of your performances". In the former example they are referring to a single performance that we would identify from context. The first sentence would be grammatically incorrect if it was referring to multiple performances.

In context TWF is clearly referring to the rules for Damage Rolls considering that is the only mention of adding your ability score modifier to damage in that chapter. The rules for Damage Rolls state:

When attacking with a weapon, you add your ability modifier--the same modifier used for the attack roll--to the damage. A spell tells you which dice to roll for damage and whether to add any modifiers.

This is a general rule about adding the ability modifier that you used to make the attack to your damage roll. TWF creates a specific exception to this particular rule. TWF does not ban adding any ability modifier from any feature or ability. If that was its intention then it would have said so clearly.

So your regular attack would be 1d?+[DEX]+[CHA] and your bonus action attack can be 1d? + [CHA].