原文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
原文Nightmare's power and toughness changes as the number of Swamps you control changes.
2013/07/01
原文The ability that defines Nightmare's power and toughness works everywhere, not just on the battlefield.
2013/07/01
原文Nightmare's ability counts all lands you control with the subtype Swamp, not just ones named Swamp.