A related concern in calculating the damage potential is does the poison stay on the short swords after the first round? I am trying to get a grip on how much damage does the NPC assassin does in the first two rounds to a creature who begins the encounter asleep. There are a couple of assassination attempts looming in our campaign that I need to get a better feel for. (This related question got me thinking).
NPC Assassin attacking first in a round (two shortswords, Multiattack)
Target is sleeping (unaware of surroundings)
A successful Dexterity (Stealth) check allows the Assassin to have surprise (but target wakes up if still alive once the attack happens).
Assassin can expect additional opposition in Round 2, and needs to finish off the target to get out for a high percentage chance of mission success.
Use average dice scores for ease of computation, since so many dice are being rolled
a. The nova damage for the NPC Assassin in Round 1.
b. The damage in round 2
Assassinate. During its first turn, the assassin has advantage on attack rolls against any creature that hasn’t taken a turn. Any hit the assassin scores against a surprised creature is a critical hit.
1 Sneak Attack (4d6), 2 hits with short sword, two saves versus poson.
Shortsword. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 24 (7d6) poison damage on a failed save, or half as much damage on a successful one.
This is for me the tricky part. I don't think the poison gets doubled due to having a saving throw, similar to a giant scorpion's stinger. (Poison's a rider). It isn't clear to me that the poison stays on the shortswords once the first attacks/hits with the short swords are completed.
Key issues to resolve:
Is the poison still on the blades in round 2?
Is the target prone (attacked with advantage) on round 2? (For reasons to answer "no" to this, please explain)
What I arrived at:
Round 1 2x((2d6) + 3) + 2x(4d6) + 14d6 (Assumes neither DC 15 con save is made)
Round 2 (no crit assumed): 2x((1d6)+3) + 4d6 + 14d6. (Assumes neither DC 15 Con save is made)
That gets me to (26d6 + 6) + (20d6 + 6) = 46d6 + 12 = 173. (Each Con save versus poison reduces this by 12.25). Four saves drops it to 32d6 + 12 = 124.
The proposed target has 112 HP, which means the result is 'insta-kill' unless the die rolls are horrible on four attacks with advantage.
What I need from an answer
Have I correctly calculated the damage done in two rounds if both attacks hit in each round?
Is the target remaining prone for round two a poor, or a valid, assumption?
Does the poison stay on the blades for the second round's attacks?
If it does not, the numbers reduce significantly.