How Does Deflect Attacks interact with attacks that force saving throws?

Question

The monk's Deflect Attacks feature reads (in part)

When an attack roll hits you and its damage includes Bludgeoning, Piercing, or Slashing damage, you can take a Reaction to reduce the attack’s total damage against you. The reduction equals 1d10 plus your Dexterity modier and Monk level. If you reduce the damage to 0, you can expend 1 Focus Point to redirect some of the attack’s force.

Consider an attack like the Giant Centipede's Bite:

Hit: 4 (1d4 + 2) piercing damage, and the target must succeed on a DC 11 Constitution saving throw or take 10 (3d6) poison damage. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.

How does a monk using deflect attacks against this work? There's a couple of different points that are unclear:

• If the monk uses deflect attacks before rolling the Con save, and they successfully reduce the damage to 0, do they still have to make the save?
  • If so, does any leftover damage prevention apply to the poison damage, or is it wasted?
• If the monk uses deflect attacks after failing the Con save, can they apply the prevention to the poison damage?
• How is it determined what order the deflect attacks happen in? Is it always in one specific order? Is it based off of when the monk decides to use it (and if so, can they choose after seeing the result of the save)? Is it determined using the rules for simultaneous effects (the player/NPC whose turn it is chooses)?

Answer 1

You first resolve the attack’s total damage, then use Deflect Attacks

If the monk uses deflect attacks before rolling the Con save, and they successfully reduce the damage to 0, do they still have to make the save?

There is no using deflect attacks before rolling the con save. The structure of attacks is explained under Making an Attack on p. 24, PHB, and it says:

3. Resolve the Attack. Make the attack roll, as detailed earlier in this chapter. 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.

Rolling the damage is part of resolving the attack. There are no separate steps for attack roll and damage roll. Both are part of the resolution step. So you first resolve the attack, including its special rules, to determine the total damage. Then, when total damage has been determined, you can use your Reaction to try and deflect the attack.

You also can see that this is how it must work by the fact that the feature reduces the attack's total damage. So you first have to figure out what the total damage is.

If so, does any leftover damage prevention apply to the poison damage, or is it wasted?

The damage reduction applies to the total damage of the attack, that is, the total of both piercing and poison damage, after you made your save and determined what that total is. You need to prevent enough damage to reduce that total to 0 to be able and spend Focus to redirect any damage.

If the monk uses deflect attacks after failing the Con save, can they apply the prevention to the poison damage?

Yes, that is how it works.

How is it determined what order the deflect attacks happen in? Is it always in one specific order? Is it based off of when the monk decides to use it (and if so, can they choose after seeing the result of the save)? Is it determined using the rules for simultaneous effects (the player/NPC whose turn it is chooses)?

You always first resolve the attack fully to determine its total damage, and only then you can use your Reaction to deflect it.

Answer 2

RAW -

1. FIRST: You deal with the bite and the deflection of the melee attack of the bite. "If you reduce the damage to 0, you can expend 1 Focus Point to redirect some of the attack’s force." So given your character has reduced the melee bite's damage to 0, you successfully deflect the attack against you and the resultant poison.
2. SECOND: You then can redirect the some of the force, by expending 1 focus point, much like the energy suit of Black Panther [but instead it is stored in the reflexes of the monk using the force and redirecting it against another] "to a creature you can see within 5 feet..."

This damage is based upon your "two rolls of your Martial Arts die plus your Dexterity modifier." This is redirected force and would not convey the poison of the Giant Centipede's bite to the creature of your redirection.

Therefore the Con save does not apply to either the monk who deflected the attack, nor the target of the redirected force from the monk.

Leftover damage prevention is not a factor as:

1. Damage from the bite to monk is deflected.
2. Damage to adjacent creature is from monk's Martial Arts and Dexterity.