Destroy target creature. Its controller discards a card.
10/1/2012 You must be able to target a creature to cast Assassin’s Strike.
10/1/2012 If the creature is an illegal target when Assassin’s Strike tries to resolve, it won’t resolve and none of its effects will happen. Its controller won’t discard a card.
7/1/2013 If Assassin’s Strike resolves but the creature isn’t destroyed (perhaps because it regenerated or has indestructible), its controller will discard a card.