Text (ET): ~this~ deals 4 damage to target creature or player. ; At the beginning of your upkeep, if an opponent has no cards in hand, you may return ~this~ from your graveyard to your hand.
It checks the number of cards in the opponents hand both when it triggers and before resolution. [Eventide FAQ 2008/07/08]
You don't pick an opponent, it checks all opponents. [Eventide FAQ 2008/07/08]
