In the module The Forge of Fury (tiny spoiler) there is a Duergar Spy creature. Its statblock is on p. 234 of Tales from the Yawning Portal.
I am interested in the way two of its features interact with each other, Enlarge and Sneak Attack. If the Spy qualifies for a Sneak Attack while Enlarged, are the damage dice added from the sneak attack doubled?
The duergar spy’s Enlarge action says:
For 1 minute, the spy magically increases in size […] While enlarged, the spy is Large, doubles her damage dice on Strength-based weapon attacks, and makes Strength checks and saving throws with advantage.
Its Sneak Attack trait says:
Once per turn, the spy can deal an extra 7 (2d6) damage when it hits a target with a weapon attack and has advantage on the attack roll, or when the target is within 5 feet of an ally that isn’t incapacitated and the spy doesn’t have disadvantage on the attack roll.
The spy has a Shortsword attack. A Shortsword is normally a finesse weapon, meaning one can use either Str or Dex for to hit and damage. The stat block suggests the Spy uses Dex, but explicitly applies Enlarge to it (the spy has a Str mod of +0 and a Dex mod of +3).
Shortsword. Melee Weapon Attack: +5 to hit. Hit: 6 (1d6+3) piercing damage, or 10 (2d6+3) while enlarged.