See the Unwritten

• WWizards of the Coast2014-09-20
  Official Ruling
  Because you’re not casting the creature cards, you can’t pay any additional or alternative costs. You can’t put the cards onto the battlefield face down.
• WWizards of the Coast2014-09-20
  Official Ruling
  You determine whether the ferocious ability applies before any creature cards are put onto the battlefield. If you put two creature cards onto the battlefield this way, those creatures enter the battlefield at the same time.
• WWizards of the Coast2014-09-20
  Official Ruling
  If a card you put onto the battlefield this way has in its mana cost, X is considered to be 0.
• 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.
• 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.

Rulings via Scryfall