Dwarven Catapult

• WWizards of the Coast2004-10-04
  Official Ruling
  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.
• WWizards of the Coast2007-09-16
  Official Ruling
  For example, if X is 5 and the targeted opponent controls three creatures, Dwarven Catapult deals 1 damage to each of those creatures.
• WWizards of the Coast2014-02-01
  Official Ruling
  If the targeted opponent controls more than X creatures, no damage will be dealt to any of them.

Rulings via Scryfall