If some but not all of Boulderfall's targets become illegal, you can't change the division of damage. Damage that would have been dealt to illegal targets simply isn't dealt.
15-09-2013
wotc
If an effect creates a copy of Boulderfall, the division of damage and number of targets can't be changed. The effect that creates the copy may allow you to change targets, however.
15-09-2013
wotc
You divide the damage as you cast the spell, not as it resolves. Each target must be assigned at least 1 damage.
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.
Ralph Horsley2013-09-27
