Rulings

• 2009-10-01
  Nightmare's power and toughness changes as the number of Swamps you control changes.
• 2013-07-01
  The ability that defines Nightmare's power and toughness works everywhere, not just on the battlefield.
• 2013-07-01
  Nightmare's ability counts all lands you control with the subtype Swamp, not just ones named Swamp.
• 2008-04-01
  If you control 0 swamps, then the Nightmare has 0 toughness and will be put into its owner's graveyard as a state-based action right before the next player gains priority.
• 2009-10-01
  Nightmare’s power and toughness changes as the number of Swamps you control changes.
• 2008-04-01
  If you control 0 swamps, then the Nightmare has 0 toughness and will be put into its owner’s graveyard as a state-based action right before the next player gains priority.
• 2013-07-01
  The ability that defines Nightmare’s power and toughness works everywhere, not just on the battlefield.
• 2013-07-01
  Nightmare’s ability counts all lands you control with the subtype Swamp, not just ones named Swamp.