How does the shared damage from the Great Old One Warlock's Thought Shield feature interact with indirect sources of psychic damage?

Question

While it can be easy to see how the Great Old One Warlock's Thought Shield feature interacts with spells that deal psychic damage or special attacks from psionic creatures, I'm not sure how to rule "second-hand" damage.

The relevant portion of the Thought Shield feature reads (PHB, p. 110):

You also have resistance to psychic damage, and whenever a creature deals psychic damage to you, that creature takes the same amount of damage that you do.

Here, my question lies in what the phrase "creature deals" is meant to be interpreted as. In my mind I'm thinking it should read closer to the Undying Warlock's Among the Dead feature (SCAG, p. 139), saying something like:

If a creature targets you directly with an attack or a harmful spell, or if it includes you in an area effect, and deals psychic damage to you, that creature takes the same amount of damage that you do.

Is it just that the latter is too wordy / rules lawyer-y? Or should premeditated damaging effects like traps, Glyph of Warding, summoned creatures, or spells cast through dummies (such as Trickery Cleric's Invoke Duplicity) have damage dealt to those who set them up too?

My group is running a multi-character Player-vs.-Player storyline that I'm helping DM, and I'm trying to get ahead before issues with our GOO-Locks crop up.

Answer 1

The rules don't answer this question explicitly, so it falls to DM ruling.

I think your interpretation:

If a creature targets you directly with an attack or a harmful spell, or if it includes you in an area effect, and deals psychic damage to you, that creature takes the same amount of damage that you do.

is a good ruling. I think it's pretty clear that psychic damage dealt by summoned creatures should reflect back on the summoned creature, and not on the summoner. And if summoned creatures work in that way, traps probably should as well.

Rules As Written, traps will not be affected by this, because (1) they aren't creatures and thus don't trigger the Thought Shield feature, and (2) objects are immune to psychic damage. A DM might nonetheless choose to narrate some Rule Of Cool effect, of the trap warping or melting or shriveling from the backlash from Thought Shield, so that the warlock feels that they got some value out of their Thought Shield power. This is harmless for single-use traps but would be a mechanics change for reuseable traps.

If a DM did choose to rule that psychic damage from traps should reflect back on the trapmaker, that DM should keep in mind that this ability probably requires line of effect; it's unlikely that it would function through a wall, or against a trapmaker that is miles away.

Finally, we should note that very few things deal psychic damage at all, and in particular most summoned creatures and traps do not deal psychic damage, so it's unlikely this question would come up in practice.

Answer 2

You should read the description of Thought Shield with the English meaning in mind.

The following :

You also have resistance to psychic damage, and whenever a creature deals psychic damage to you, that creature takes the same amount of damage that you do.

Can be read as :

You also have resistance to psychic damage. In addition, whenever a creature deals psychic damage to you, that creature takes the same amount of damage that you do.

In short, the resistance is not dependant on a creature dealing the damage.

The Glyph of Warding spell description states that the Spell Glyph is cast when the glyph is triggered which does not require the caster to be alive. Also, it is clear that the intent for the Glyph of Warding and the Symbol spells is that they should be used as trap and as such they should follow the rules for magical traps.

If it helps you can look at the mechanic used by the Spell Storing magic item. The spell is cast once by the original caster and a second time by someone using the magic item. In our case, the spell creates a magical trap (a glyph) that will cast the chosen spell the second time.

As for Channel Divinity : Invoke Duplicity, the caster is still the cleric. The duplicate is used to determine the point of origin of the spell. The duplicate does not actually cast the spell.

Answer 3

A spell like Glyph of Warding or Symbol would still count but a trap which doesn't use a spell cast by the creature might not.

Glyph of Warding and Symbol are spells with an inherent DC and/or spell slot spent by the casting creature. It can be tied directly back to the creature who cast it and as such Thought Shield can trigger because while still technically a spell dealing damage a creature was responsible for casting that spell.

A trap with an incidental psychic damage effect such as an obelisk that blasts any creature that steps into it's range with psychic damage which has been set up by another creature isn't an effect which ties directly back to them. The damage, while intended, is not being directly dealt by the creature who set it up but rather by an object.

Answer 4

Your reading is correct

"A creature deals damage" means the damage must come directly from that creature. Summoning monsters, placing traps, dropping caltrops, are not direct methods of damage.

• In the case of Symbol, and Glyph of Warding the glyphs deal the damage, not the creature that inscribed them.
• In the case of summoned creatures, those summons deal the damage.
• In the case of Invoke Duplicity, you are casting as if you were in the illusions space, so you are still the one dealing the damage.