Monstrous Onslaught deals X damage divided as you choose among any number of target creatures, where X is the greatest power among creatures you control as you cast this spell.
You divide the damage among the target creatures as you cast Monstrous Onslaught. Each target must be assigned at least 1 damage.
10-11-2020
wotc
The value of X is determined at the time you divide damage. It won't change later, even if the greatest power among creatures you control changes.
10-11-2020
wotc
If some of the targets become illegal, the original division of damage still applies. The damage that was divided among the illegal targets simply isn't dealt; it isn't re-assigned to remaining legal targets.
10-11-2020
wotc
The damage is dealt by Monstrous Onslaught, not by the creature with the greatest power among creatures you control.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.