Does the poison damage from a Naga Monk's bite scale?

Question

I'm building a naga monk (using the statistics from Plane Shift: Amonkhet), and the bite attack states that:

Natural Weapons. Your fanged maw and constricting serpentine body are natural weapons, which you can use to make unarmed strikes. If you hit with your bite, you deal piercing damage equal to 1d4 + your Strength modifier, and your target must make a Constitution saving throw (DC 8 + your proficiency bonus + your Constitution modifier). On a failed save, the target takes 1d4 poison damage. [...]

It makes sense for the piercing damage to scale, and for the bite to become Dex-based. However, I can't find anything that says whether Martial Arts allows the 1d4 poison damage to scale.

Answer 1

You're reading things correctly

The Martial Arts feature only scales your damage from attacks that are made with either unarmed strikes and monk weapons. The poison rider is an add-on effect which is only inflicted on a failed save, while the trigger for that save is due to a successful hit, it itself isn't due to a weapon's damage roll from the Martial Arts feature.

The relevant parts of the Martials Arts rules are below (emphasis mine):

You gain the following benefits while you are unarmed or wielding only monk weapons and you aren’t wearing armor or wielding a shield:

• You can use Dexterity instead of Strength for the attack and damage rolls of your unarmed strikes and monk weapons
• You can roll a d4 in place of the normal damage of your unarmed strike or monk weapon. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.

In other words, the series of events are:

1. Make an attack roll using Dexterity per the Martial Arts feature.
2. If it hits, roll your Martial Arts damage die, also as per the Martial Arts feature.
3. From your specific character's racial feature, the opponent then rolls a Constitution save. If they fail, they are subject to the poison damage.

The cause of the poison's damage has nothing to do with the Martial Arts feature. It is only because of your racial feature that the opponent may be subject to poison damage, it has nothing to do with the Martial Arts feature and thus doesn't scale per that feature.

Answer 2

Martial Arts does not apply to the poison damage

As explained in detail in If an attack causes additional damage after a saving throw, is it counted as a separate source of damage for the purpose of failed death saves?, the secondary damage caused by the poison is considered a separate source of damage.

The rules for resolving attacks state:

3. Resolve the attack. You make the attack roll. On a hit, you roll damage, unless the particular attack has rules that specify otherwise. Some attacks cause special effects in addition to or instead of damage.

The attack here causes a special effect (a poison save), in addition to the damage it does. That effect in turn may deal damage, if the save is not made. But that is not directly damage from the attack any more, it is a new source of damage. Therefore, Martial Arts does not apply to it.