What modifiers are added to the attack and damage rolls of this unique longbow from Waterdeep: Dragon Heist?

Question

There is a unique longbow in the Waterdeep: Dragon Heist module (p. 201), whose description includes:

This unique weapon can be used only by a Medium or larger creature that has a Strength of 18 or higher. The bow shoots oversized arrows that deal piercing damage equal to 2d6 + the wielder's Strength modifier...

However when looking at the PHB's section on "Dexterity Attack Rolls and Damage", I realized it states:

You add your Dexterity modifier to your attack roll and your damage roll when attacking with a ranged weapon...

To me this means that unless a feature specifically tells you not to, you would add your Dexterity modifier to a ranged weapon's damage and attack rolls.

An example of such a prevention is Two-Weapon Fighting which states:

You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative.

Notably, the NPC who owns it has a +3 proficiency bonus, a +7 to attacks with the longbow and deals 2d6+4 damage. Unfortunately, their strength and dexterity modifiers are both +4 so I can't tell which is being added.

However, as @thedarkwanderer pointed out in a comment in the Q/A "How can I shoot a bow using strength instead of dexterity?":

NPCs use different rules than PC's

This leaves me uncertain and with the following question:
If a PC wields this unique longbow, what modifiers do they add to its attack and damage rolls?

Answer 1

When the text is unclear, look for examples

Surprisingly this relies more on text interpretation than rule interpretation, which is probably where the confusion lies.

Normally a weapon description would list a die number (1d6, 2d6, 1d4, etc.) in a table for the damage numbers. From there it was on the player to know to add your ability modifier based on the attribute used for the attack roll (PHB 194). Unfortunately the damage for this weapon is described inline with the weapon description.

The bow shoots oversized arrows that deal piercing damage equal to 2d6 + the wielder's Strength modifier

has two possible interpretations:

1. 2d6 + STR is the weapon's base damage and you should add your Dexterity in addition to this
           ^{(if a weapon description said "...piercing damage equal to 1d10+1" then you would expect to add dexterity, after all)}
2. 2d6 + STR replaces the final damage value of a normal bow attack: 2d6 + DEX.

Both of which are valid. In this case the confusion lies in the flavorful wording mixed with attribute modifiers being unusual for weapon damage descriptions.

Use the NPC as an example of the intended usage

The NPC using this bow is an example straight from the designers about how this bow should work and can help us at this impasse. You cite that they are listed as having attacks from the bow with damage equal to 2d6+4, and they have a Strength and Dexterity modifier of +4. Because it is not a +8, we can infer that the bow is intended to use STR instead of DEX and not STR in addition to DEX in the hands of a player. A more accurate version of the text might read:

Attacks made with this bow deal 2d6 piercing damage and adds the wielder's Strength modifier instead of their Dexterity modifier.

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The Attack Roll

The PHB(194) has this to say about the ability modifier for Attack Rolls:

The ability modifier used for a melee weapon attack is Strength, and the ability modifier used for a ranged weapon attack is Dexterity. Weapons that have the finesse or thrown property break this rule.

However there is some debate surrounding page 196 where, while talking about Damage Rolls, the PHB says:

When attacking with a weapon, you add your ability modifier--the same modifier used for the attack roll--to the damage.

Where it could be implied that the ability modifier and the attack modifier must match. Because the former statement regarding the attribute-to-range assignment is explicit, directly under the heading regarding attack rolls, and specifically mentions exceptions to the rule, I don't consider the justification strong enough to imply that the weapon would use Strength as the attack modifier because of the excerpt on page 196. It appears to have been meant only to tell the reader that the damage roll attribute normally depends on the Attack roll attribute.

Neither the NPC description nor the weapon description mention explicitly a different attack attribute modifier, and there is no rule stating explicitly that attack attribute modifiers must correspond to the damage attribute modifier.

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We are left with the following: The general rule for ranged weapon attack modifiers using Dexterity applies, with an intentional override changing the damage roll modifier from Dexterity (as would normally be inherited from the Attack Roll) to Strength. The bow makes attack rolls adding Dexterity and damage rolls adding Strength.

Answer 2

Specific trumps general

The general rule for Dexterity-based attacks is that you add your Dexterity modifier to the damage if you hit. The rules for weapons list the basic damage for each, and you add your Strength or Dexterity bonus when applicable.

That specific longbow, however, states that the damage it does is 2d6 + the wielder's Strength modifier. That is a specific rule which overrides the general rule.

As such, you use Dexterity for the attack roll and Strength for the damage roll.

Answer 3

You use your Strength modifier for the attack roll and the damage roll

The section in the PHB on Damage Rolls states (emphasis mine):

When attacking with a weapon you add your ability modifier - the same modifier used for the attack roll - to the damage.

So the general rule is that the damage roll uses the same ability modifier as the attack roll.

In this case we are given a modified damage modifier (ie it uses Strength instead of the normal Dexterity). In the absence of any other information to the contrary we should apply the above general rule that the damage modifier is the same as the attack modifier.

Thus, in the absence of any other information, by modifying the modifier for the damage roll, the item also modified the ability modifier for the attack roll.

Using this information and looking at the Stat Block of the Creature using the unique longbow provides the answers to your question:

Oversized Longbow. Ranged Weapon Attack: +7 to hit, range 150/600ft., one target. Hit: 11 (2d6 + 4) piercing damage.

The +7 is the +4 strength modifier, combined with the creatures proficiency bonus (+3). the damage modifier is also their Strength modifier (+4).

But there is a second general rule for ranged weapons that we are ignoring here...that ranged weapons use Dexterity for their attack rolls. Why are we disregarding this?

The wording of this item has put us into conflict betwen two general rules, with no clear way to resolve it. The general rules in question are:

Ranged Attack rolls use Dexterity as the to hit bonus (General 1):

You add your Dexterity modifier to your attack roll and your damage roll when attacking with a ranged weapon [...]

Damage Rolls use the same modifier as the attack roll (General 2):

When attacking with a weapon you add your ability modifier - the same modifier used for the attack roll - to the damage.

D&D is an exceptions based game, and the normal way to resolve this would be to use the specific beats general principle. However in this case we do not have enough information to do this effectively (hence the divided debate here!).

As written, the weapon just says damage is 2d6 + Strength. It doesn't say if this is due to the attack modifier having been changed (in the background as a specific exception to General 1) and the damage simply flowing through, or the damage modifier being changed in isolation (as a specific exception to General 1).

Thus we have two options:

Interpretation A: The attack modifier is Dexterity, and the item description is a specific exception to General 2

Interpretation B: The attack uses Strength because the item description is a specific exception to General 1

If we use Interpretation A then we arrive at @AllanMills answer.

If we use Interpretation B then we arrive at my answer.

The consequence of Interpretation A is that this unique longbow is significantly more difficult for the player and the DM to run and not make a mistake.

The consequence of Interpretation B is that the unique longbow is just as easy to run as a regular longbow, but with the ability modifier changed from Dexterity to Strength.

But don't NPCs have different rules to PCs for weapons?

No they do not. In the DMG on page 278 the rules for weapons wielded by monsters are:

If a monster wields a manufactured weapon, it deals damage appropriate to the weapon. For example, a greataxe in the hands of a Medium monster deals 1d12 slashing damage plus the monster's Strength modifier, as is normal for that weapon.

Big monsters typically wield oversized weapons that deal extra dice of damage on a hit. Double the weapon dice if the creature is Large, triple the weapon dice if it's Huge, and quadruple the weapon dice if it's Gargantuan. For example, a Huge giant wielding an appropriately sized greataxe deals 3d12 slashing damage (plus its Strength bonus), instead of the normal 1d12.

A creature has disadvantage on attack rolls with a weapon that is sized for a larger attacker. You can rule that a weapon sized for an attacker two or more sizes larger is too big for the creature to use at all.

From this we see, that if the NPC/Monster is medium size, they would use the normal weapon rules in the PHB. If the NPC is a Large or bigger creature, wielding an appropriately sized weapon for their size (Large creature => Large weapon, Huge creature => Huge weapon) then the damage dice for the oversized weapon are modified.

Should a creature wield a weapon that is too large for it, they either have disadvantage on the attack, or are unable to wield the weapon entirely (barring some feature that would enable them to).

Answer 4

It's unclear from the text

Normally you'd use your Dexterity for the attack, but normally the damage roll uses the same modifier as the attack roll (implying that you should use Strength for the attack). It's not clear which of these rules should override the other one.

When the rules are unclear, we on StackExchange can't and shouldn't issue rulings for you. That's the job of your DM.

You'll have to ask your DM. : )

Answer 5

You add your Dexterity to the attack roll, because the weapon doesn't say otherwise so the rules on Ranged Attacks still hold.

For the damage roll, however, it seems like you are supposed to add both Strength and Dexterity for the damage roll. Reading the item's unique features, you get to add your STR to the damage as an additional modifier, and then you can add DEX as normal from hitting a ranged weapon. Phb 196 on Damage Rolls supports this:

You roll the damage die or dice, add any modifiers, and apply the damage to your target. Magic weapons, special abilities, and other factors can grant a bonus to damage.

So it's no different from adding fire damage from a magical weapon or any other bonus.

The feature would tell you if you add STR instead of DEX for damage. Features like Shillelagh say this explicitly:

... For the duration, you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon

Answer 6

The weapons entry states that the weapon's damage is (2d6+STR) in the same way that a longbow's damage is (1d8). RaW the bow has no traits that would indicate it uses str to make attack rolls (as is explicit in the thrown property) so the attack roll uses dex. Total damage of the attack is a distinct element from a weapons damage rating.

A+B+C=D A=(weapons damage) B=(attackers relevant ability modifier) C=(Misc modifiers such as magical bonuses) D= Total Damage

Because the weapon says nothing explicit about what is presented being an alternative A+B+C with which to calculate D, then you have to take what's presented to be equivalent to what it is for other weapons (just the "A"). In this case, though, it looks a bit like Algebra, and the weapon's damage "rating" is explicit, specific, an exception- In other words, it trumps the norm that says a weapon damage rating has to be only made up of dice.

We plug in "2D6+STR" in for "A," yes because as written, it defines A and not A+B

(2D6+STR) + (Dex Ability Mod)+ (Misc other bonuses) = The attacks total damage

The monster's stat block shows us this wasn't likely the intention, but as is, it is the stat block that was incorrectly calculated intentions be damned. Something that should require errata, but until then = RaW.