Nightmare

Creature — Nightmare Horse    (CMC:6)

Flying (This creature can't be blocked except by creatures with flying or reach.) Nightmare's power and toughness are each equal to the number of Swamps you control.

The thunder of its hooves beats dreams into despair.

107 M10 • ENCarl Critchlow

™ & © 1993—2009 Wizards of the Coast

Legal in: Standard,Modern,Legacy,Vintage,Commander

Oracle Text (click to copy):

Nightmare {5}{B} Creature — Nightmare Horse Flying (This creature can't be blocked except by creatures with flying or reach.) Nightmare's power and toughness are each equal to the number of Swamps you control. ★/★

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4/1/2008
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.
10/1/2009
Nightmare's power and toughness changes as the number of Swamps you control changes.
7/1/2013
The ability that defines Nightmare’s power and toughness works everywhere, not just on the battlefield.
7/1/2013
Nightmare’s ability counts all lands you control with the subtype Swamp, not just ones named Swamp.

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