How does the vulnerability from the Tomb of Levistus warlock invocation interact with the resistance from the tiefling's Infernal Legacy trait?

Question

The description of the warlock's Tomb of Levistus eldritch invocation says (Xanathar's Guide to Everything, p. 57; emphasis mine):

As a reaction when you take damage, you can entomb yourself in ice, which melts away at the end of your next turn. You gain 10 temporary hit points per warlock level, which takes as much of the triggering damage as possible. Immediately after you take the damage, you gain vulnerability to fire damage, your speed is reduced to 0, and you are incapacitated. These effects, including any remaining temporary hit points, all end when the ice melts.

The tiefling's Infernal Legacy racial trait grants fire resistance.

For a tiefling warlock with the Tomb of Levistus invocation, how would this eldritch invocation (specific) interact with this racial feat (general)?

• Do they cancel?
• Or does the magic of the Tomb of Levistus invocation (specific) overpower the Infernal Legacy trait (general) completely?

Which applies here? General vs. specific rules, or resistance vs. vulnerability rules?

Answer 1

Vulnerability and Resistance are not mutually exclusive so there is no general vs specific

The general/specific rule only applies when two rules couldn't occur simultaneously such as two things changing your Strength score, or one thing making you prone and the other explicitly making you not prone. However, with vulnerability and resistance, there is no such clause or requirement and in fact there exists the following quote:

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

- Player's Handbook (page 197)

The fact that they apply in an order shows that a creature can be affected by both at once. What this means is that odd damage values will lower by one and even damage values will remain the same. Again, this only occurs because nothing in the rules actually prevents you from having both resistance and vulnerability simultaneously and so the specific/general rule never applies.

Answer 2

Resistance and vulnerability, while doing directly opposite things, aren't contradicting effects. They stack to a net zero effect (ignoring rounding).

This is similar to having advantage and disadvantage at the same time, or having both a +2 and -2 to a roll. Two effects interacting with the same thing is not necessarily a matter of specific versus general, only when they contradict in a non-stackable way.

Answer 3

If the incoming damage that triggers it is fire damage, the Tiefling gets fire resistance for that attack to reduce the amount of fire damage that is done to the temporary hit points.

Immediately after you take the damage, you gain vulnerability to fire damage,

You forgot the immediately after you take the damage part, so that vulnerability would not count on the triggering damage, and basically nullify the resistance for any other incoming fire damage. If you doubled the damage first (vulnerability) then applied the resistance, you can dodge the messy odd damage throwing off the fire damage by 1. That would be a house rule though, you are supposed to do resistance first, then round down if necessary, then double it so a 11 damage fire attack would get cut in half to 5.5, rounded down to 5 then doubled back to 10, if you follow the rules.