You choose the value of X, the targets, and how damage will be divided as you cast Nahiri's Sacrifice.
2023-02-04 • wotc
You can't choose more than X targets, and each chosen target must receive at least 1 damage.
2023-02-04 • wotc
If some of the targets of the last ability become illegal, the original division of damage still applies, but the damage that would have been dealt to illegal targets isn't dealt at all.