Roaring Primadox

• WWizards of the Coast2012-07-01
  Official Ruling
  Roaring Primadox’s ability is mandatory. When it resolves, if Roaring Primadox is the only creature you control, you must return it to its owner’s hand.
• WWizards of the Coast2014-07-18
  Official Ruling
  The ability doesn’t target any creature. You choose which one to return when the ability resolves. No player can respond to this choice once the ability starts resolving.

Rulings via Scryfall