Grave Exchange

Oracle Text

Return target creature card from your graveyard to your hand. Target player sacrifices a creature.

Card Rulings

5/1/2012 Grave Exchange targets both a creature card in your graveyard and a player. You can’t cast it unless there is a legal target to choose for both. You can target a player who controls no creatures.
5/1/2012 If both targets are illegal when Grave Exchange tries to resolve, it won’t resolve and none of its effects will happen. If only one target is legal, the effect relevant to that target will happen and the other will not.