2004-10-04 : Count the number of creatures on resolution of the spell and divide X by that number at that time. If the number of creatures changes before resolution, the damage done may be different than what you expected.

2007-09-16 : For example, if X is 5 and the targeted opponent controls three creatures, Dwarven Catapult deals 1 damage to each of those creatures.

2014-02-01 : If the targeted opponent controls more than X creatures, no damage will be dealt to any of them.