Spoils of War | Magic: The Gathering
Formats Spoils of War is Legal in
Official Oracle Text for Spoils of War
Distribute X +1/+1 counters among any number of target creatures.
—Ib Halfheart, Goblin Tactician
Official Rulings for Spoils of War
8/1/2008 : X is set as you cast the spell to be exactly the number of appropriate cards in an opponent's graveyard. You can't choose a higher or lower value for X.