You announce how the damage will be divided as part of casting Spreading Flames. Each chosen target must receive at least 1 damage.
13-07-2016
wotc
If Spreading Flames has multiple targets, and some, but not all, are illegal targets when Spreading Flames tries to resolve, Spreading Flames will still deal damage to the remaining legal targets according to the original damage division. If all the targets are illegal, the spell won’t resolve.
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.