Whenever this creature becomes blocked, each creature blocking it gets -1/-1 until end of turn.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Whenever this creature becomes blocked, each creature blocking it gets -1/-1 until end of turn.
Whenever a creature blocking this creature dies, that creature's controller loses 1 life.
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)