In the module The forge of fury (Small spoiler) There is a Dery Spy creature. His statblock is on p. 234 of Tales from the yawning portal.
I'm 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 it is Extended, do the damage dice of the sneak attack double?
The action of Enlarge of the spy duergar says:
For 1 minute, the spy magically increases in size. […] While it is enlarged, the spy is Great, doubles its damage dice in the attacks with weapons based on the Force and makes Force controls and saves shots with advantage.
His sneak attack feature says:
Once per turn, the spy can inflict additional damage of 7 (2d6) when he hits a target with a weapon attack and has an advantage in the attack roll, or when the target is within 5 feet of an ally that is not incapacitated and the Spy has no disadvantage in the attack roll.
The spy has a Shortsword attack. A Shortsword is usually a delicate weapon, which means that one can use Str or Dex to hit and damage. The block of statistics suggests that the Spy uses Dex, but it is explicitly applied to Enlarge (the spy has a mod Str +0 and a mod Dex +3).
Short sword Melee weapon attack: +5 to hit. Hit: 6 (1d6 + 3) of piercing damage, or 10 (2d6 + 3) while enlarged.