How does the Dwarven Resilience trait interact with the Prismatic Spray spell if the target is struck by two rays and only one does poison damage?

Question

The prismatic spray spell can do different damage types (and status effects) depending on a d8 roll for the target that determines which ray targets each creature in the area of effect.

Say the target is a dwarf, and thus has the Dwarven Resilience trait. The caster rolls an 8 initially (causing the target to be struck by two rays instead), and then one of the two rerolls is a 4, which causes poison damage? Since Dwarven Resilience provides "advantage on saving throws against poison" (not just advantage against being poisoned, as protection from poison does), the dwarf should get advantage on the save - even though the effect of the other ray might not be poison-related.

Is my interpretation of the sequence of events correct?

Answer 1

No, the Dwarf does not get advantage. The saving throw is not against poison, it's against the rays.

However, for any poison damage they do take as a result of being struck by these rays, they only take half damage (quarter damage if they made the save).

Example 1, 1 poison ray:

• No advantage on save
• 20 damage rolled
• If they make the save, they take 5 damage
• If they fail the save, they take 10 damage

Example 2, 1 poison, 1 fire ray:

• Still no advantage
• 20 damage for each ray
• If they make the save, they take 10 + 5 = 15 damage
• If they fail the save, they take 20 + 10 = 30 damage.

Answer 2

No, the dwarf shouldn't get advantage on the saving throw.

The saving throw against prismatic spray is for dodging the ray that is delivering the poison, not the poison itself. Because there is no saving throw for being affected by the poison, there is no advantage to be gained.

The poison damage does get halved the way Mike Caron showed, though.