Does a Shadow double Strength damage on a Critical Hit?

Question

I had a situation come up in the last session I ran (four times, no less).

When a Shadow lands a critical hit, is the strength damage dice also multiplied?

At the time I ruled no, but that had more to do with the fact that the party was getting creamed, rather than anything rules based. While I know extra dice of damage like smite and sneak attack are doubled, the strength damage isn't health damage, but it is still a rolled dice. And there isn't a huge precedent for that in 5e to compare against.

Answer 1

No, the Strength reduction isn't increased.

Critical hits say the following:

When you score a critical hit, you get to roll extra dice for the attack’s damage against the target. Roll all of the attack’s damage dice twice and add them together. Then add any relevant modifiers as normal. To speed up play, you can roll all the damage dice at once.

For example, if you score a critical hit with a dagger, roll 2d4 for the damage, rather than 1d4, and then add your relevant ability modifier. If the attack involves other damage dice, such as from the rogue’s Sneak Attack feature, you roll those dice twice as well.

And the Shadow's Strength Drain ability reads as follows:

Strength Drain. Melee Weapon Attack: +4 to hit, reach 5ft., one creature. Hit: 9 (2d6 + 2) necrotic damage, and the target's Strength score is reduced by 1d4.

Note the key phrasing here: "the target's Strength score is reduced by 1d4", not, e.g., "the target takes 1d4 Strength damage". There's no concept of ability damage in 5e. The Strength reduction isn't any kind of damage, so it isn't multiplied on a critical hit.