MTG Keyword Rules — Comprehensive Rules Glossary

Daybound and nightbound are found on opposite faces of some double-faced cards (see rule 712, “Double-Faced Cards”).

Daybound is found on the front faces of some double-faced cards and represents three static abilities. “Daybound” means “If it is night and this permanent is represented by a double-faced card, it enters transformed,” “As it becomes night, if this permanent is front face up, transform it,” and “This permanent can’t transform except due to its daybound ability.” See rule 731, “Day and Night.”

Any time a player controls a permanent that is front face up with daybound and it’s night, that player transforms that permanent. This happens immediately and isn’t a state-based action.

Any time a player controls a permanent with daybound, if it’s neither day nor night, it becomes day.

Nightbound is found on the back faces of some double-faced cards and represents two static abilities. “Nightbound” means “As it becomes day, if this permanent is back face up, transform it” and “This permanent can’t transform except due to its nightbound ability.”

Any time a player controls a permanent that is back face up with nightbound and it’s day, that player transforms that permanent. This happens immediately and isn’t a state-based action.

Any time a player controls a permanent with nightbound, if it’s neither day nor night and there are no permanents with daybound on the battlefield, it becomes night.