[RPG] Does the Grave Cleric’s “Path to the Grave” feature replace a creature’s damage immunity with vulnerability


Let's say a creature (like a devil) is normally immune to fire damage. The unfortunate devil is within 30ft of a Grave Cleric and their Sorcerer friend.

The Grave Cleric uses their Path to the grave feature:

As an action, you choose one creature you can see within 30ft of you, cursing it until the end of your next turn. The next time you or an ally of yours hits the cursed creature with an attack, the creature has vulnerability to all of that attack's damage, and then the curse ends.

Is the devil still immune? Or are they instead vulnerable to the damage?

To put it another way, does the Path to the Grave replace the immunity with a vulnerability? Or does it add a vulnerability on top of the immunity?

Note: The linked question is asking "what happens if a creature somehow has both immunity and vulnerability" (presupposing that they can get into that situation in the first place). This question isn't making that presupposition, in fact it's explicitly asking if that presupposition can even happen.

Best Answer

Adding vulnerability doesn't remove immunity

There's nothing in the rules about any of vulnerability, resistance, or immunity being mutually exclusive. In fact, in the case of vulnerability and resistance, the rules explicitly cover the case of a creature having both (emphasis added):

Resistance and then vulnerability are applied after all other modifiers to damage.

Given that resistance and vulnerability are allowed to co-exist, and given that there is no specific rule preventing vulnerability and immunity from co-existing, the reasonable ruling is that vulnerability and immunity can also co-exist. (Most likely, there is no specific rule for this because there is no ambiguity: the damage is always zero regardless of which order you apply them in.) Hence, if a creature has immunity to a damage type, giving it vulnerability to the same damage type doesn't negate that immunity.

XGtE explicitly allows for all 3 damage modifiers to coexist

The section on resistance and vulnerability in the introduction to Xanathar's Guide to Everything makes this coexistence explicit:

Here’s the order that you apply modifiers to damage: (1) any relevant damage immunity, (2) any addition or subtraction to the damage, (3) one relevant damage resistance, and (4) one relevant damage vulnerability.

(Thanks to Someone_evil for pointing this out.)