D&D 5E Gravetouched with multiple damage types

[ECMO3]

Question about gravetouched:

"In addition, once during each of your turns, when you hit a creature with an attack roll and roll damage against the creature, you can replace the damage type with necrotic damage. While you are using your Form of Dread, you can roll one additional damage die when determining the necrotic damage the target takes."

So what if I am using a dragontooth dagger and booming blade and blessed strikes and I hit and I have something like 1d4 piercing+1d6 acid + 2d8 thunder +1d8 radiant +4 piercing (dexterity).

Is that ALL of that damage turned into necrotic? If not can I choose which die (dice) I change?

 

[BookTenTiger]

I assume, based on the way the rule is written, that all the damage types become Necrotic.

But this is a good case for "Rulings, not Rules." I would see no issue at my table for choosing just one damage type to replace with Necrotic.

 

[Paul Farquhar]

It reads to me that only one damage roll is replaced, since it says "the" damage. I would rule that it was the primary one/the one that gets the ability score bonus. In the example above, the piercing damage. You get to roll an additional D4.

But DM's call.

 

[cbwjm]

I'd either rule that the base damage (piercing) is converted or do what BookTenTiger mentioned and make it all the damage, letting you roll an addition die of the highest one available.