I am contemplating a Oath of Conquest Paladin / Sorcerer multiclass character, with a 1 level dip in hexblade warlock.
This character will have access to the Armor of Agathys and Shield spells, which potentially allows for a pretty nice combo.
The Shield spell states (PHB 275):
Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell…
Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack,
It looks like you are indeed hit by an attack, but since you have a bonus to AC, you can potentially force that attack to miss instead.
Armor of Agathys states (PHB 215),
If a creature hits you with a melee attack while you have these hit points, the creature takes 5 cold damage.
If I cast Shield and cause an attack that "hit" me to miss, does Armor of Agathys still deal damage?
I am leaning toward yes, though this combo seems a little too strong–Shield is already a strong spell, and this character will eventually have 9 1st level spell slots and a 7th level spell slot. Not only can they freely block attacks with Shield, but they can also deal up to 35 (5d10) damage to the attacker without an attack roll or saving throw. While a Warlock would have to spend both of their spell slots to do this once, my character would be able to do this 4 times with spell slots to spare.
Some notes:
- Related questions ask about reducing the damage from a confirmed hit to zero. This question is asking about what happens when the Shield spell causes the attack to miss entirely.
- A number of online resources, such as the Roll20 5th edition compendium, seem to be missing the correct casting time for the Shield spell. Answerers should make sure they're looking at the correct version from the PHB.
Best Answer
No, armor of Agathys would not do its damage.
Shield is one of the few reaction spells that 'interrupts'/potentially cancels its trigger, as clarified by the DMG in the 'Adjudicating Reaction Timing' section:
(See also: @Rubiksmoose's answer to 'Do reactions interrupt their triggers or not?')
Since it 'interrupts' the hit and changes it to a miss, there is no longer a hit to trigger armor of Agathys's damage effect; 'interrupt' implies shield affects/changes the trigger during the triggering event and prevents it from occurring, and there's no longer a hit for the armor of Agathys to trigger off of.
Jeremy Crawford, lead rules designer of D&D5e, unofficially indicates this is the logic to follow as well in a response to a question about 'on hit' riders interacting with shield:
For an analogy, let's use another example of an interrupting reaction that's a bit more clear cut: the opportunity attack. Lets look at the timing of that trigger:
So the attack's trigger is when they move out of reach, but interrupts that movement and occurs before they've actually moved out of reach.
Let's imagine a scenario where an enemy is between a fighter and a field of spike growth, each of which are 5 feet from the enemy. The enemy runs directly away from the fighter into the spike growth field, both leaving the fighter's reach and moving into the area of spike growth at the same time.
Normally, the enemy would immediately take the 2d4 damage from the spike growth. However, the fighter decides to take an opportunity attack, hitting the enemy and knocking it out with a nonlethal attack. The enemy is now stopped exactly where it started, within 5 feet of the fighter. We would not expect it to take spike growth damage, as the enemy's movement away from the fighter/into the area of spike growth never actually happened- it was interrupted and stopped, as evidenced by the enemy remaining within its square.
To me, this same logic applies to how shield interacts with the hit it interrupts- it has no longer happened, so nothing else can trigger off of it.