Nightmare's power and toughness are each equal to the number of swamps controlled by it's controller while it's on the stack or battlefield, and by it's owner if it is in any other zone. This means that if while it's on the battlefield it's control changes (such as through Hijack) to a player who controls no swamps it will be a 0/0. A creature with 0 toughness is put into its owner's graveyard as a state based action. As it is no longer on the battlefield, it will not be returned at the end of turn when Hijack's control changing effect wears off.
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Neotrup says... Accepted answer #1
Nightmare's power and toughness are each equal to the number of swamps controlled by it's controller while it's on the stack or battlefield, and by it's owner if it is in any other zone. This means that if while it's on the battlefield it's control changes (such as through Hijack) to a player who controls no swamps it will be a 0/0. A creature with 0 toughness is put into its owner's graveyard as a state based action. As it is no longer on the battlefield, it will not be returned at the end of turn when Hijack's control changing effect wears off.
April 15, 2018 6:32 p.m.