You choose how many targets Arc Lightning has and how the damage is divided as you cast the spell. Each target must receive at least 1 damage.
20-09-2014
wotc
If some of the creatures are illegal targets as Arc Lightning tries to resolve, the original division of damage still applies but no damage is dealt to the illegal targets. If all targets are illegal, Arc Lightning doesn’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.