Target creature gains double strike until end of turn. (It deals both first-strike and regular combat damage.)
Ferocious — That creature also gains trample until end of turn if you control a creature with power 4 or greater.
11/24/2014 If all creatures blocking a creature with double strike and trample are destroyed during the first combat damage step, the creature with double strike and trample will deal all its combat damage to the defending player or planeswalker during the second combat damage step.
11/24/2014 Ferocious abilities of instants and sorceries that don’t use the word “instead” provide an additional effect if you control a creature with power 4 or greater as they resolve.