CapnZapp
Legend
You know, I read your post three times, and I still don't understand.It’s relevant because it answers your questions.
First, thanks for identifying the ability. They helps.
RAW, you total all of the damage first from a single attack. Then you apply all immunities, then all modifiers, then one resistance, then (in your case with the troll) one vulnerability.
The resistance and/or vulnerability applies to all of the damage that makes it through the other steps.
Likewise, the barbarian ability reduces the damage from the entire attack (apply all modifiers). So the DM in question is “doing it wrong” RAW.
This is for simplicity best I can tell. The times where the different damage types really make that much of a difference are few, and starting with the total for the single attack and then adding modifications streamlines things.
Where in your post do you even address the issue. (Granted, I'm late to this party so maybe you have already stated your position earlier, I didn't reread the whole thread, it got too confusing)
In my example, do you end up with 3 or 1 damage? Does fire resistance help or not? What page do you point to for your answer?
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