Nightshade Assassin | Magic: The Gathering
Formats Nightshade Assassin is Legal in
Official Oracle Text for Nightshade Assassin
When Nightshade Assassin enters the battlefield, you may reveal X black cards in your hand. If you do, target creature gets -X/-X until end of turn.
Madness (If you discard this card, you may cast it for its madness cost instead of putting it into your graveyard.)
Official Rulings for Nightshade Assassin
9/25/2006 : You may choose to reveal X black cards in your hand, then choose X to be 0.