Crater's Claws

• WWizards of the Coast2014-09-20
  Official Ruling
  Ferocious abilities of instants and sorceries that don’t use the word “instead” will provide an additional effect if you control a creature with power 4 or greater as they resolve.
• WWizards of the Coast2014-09-20
  Official Ruling
  If you control a creature with power 4 or greater, Crater’s Claws with X equals 0 will deal 2 damage, with X equals 1 will deal 3 damage, and so on.
• WWizards of the Coast2014-09-20
  Official Ruling
  Some ferocious abilities that appear on instants and sorceries use the word “instead.” These spells have an upgraded effect if you control a creature with power 4 or greater as they resolve. For these, you only get the upgraded effect, not both effects.

Rulings via Scryfall