2016-04-08 : Compelling Deterrence targets only the nonland permanent. If that permanent becomes an illegal target, Compelling Deterrence doesn’t resolve and that player doesn’t discard a card.

2016-04-08 : If you target the only Zombie you control with Compelling Deterrence, you won’t discard a card.

2016-04-08 : The card returned to its owner’s hand may be the card they discard. If it’s the only card in that player’s hand, it must be discarded.