Crater's Claws

Crater's Claws deals X damage to any target.
Ferocious — Crater's Claws deals X plus 2 damage instead if you control a creature with power 4 or greater.

Khans of Tarkir

Khans of Tarkir Promos

Crater's Claws deals X damage to target creature or player.
Ferocious — Crater's Claws deals X plus 2 damage to that creature or player instead if you control a creature with power 4 or greater.

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.

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.

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.