Oracle Text

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)

When Skullwinder enters the battlefield, return target card from your graveyard to your hand, then choose an opponent. That player returns a card from their graveyard to their hand.

Card Rulings

11/4/2015 Skullwinder’s enters-the-battlefield ability targets only the card in your graveyard. If that card is an illegal target as the ability tries to resolve, the ability won’t resolve and none of its effects will happen. No cards will be returned to any player’s hand.
11/4/2015 You choose the opponent as the ability is resolving. You may choose an opponent with no cards in their graveyard.