If it is night, and the active player of the previous turn cast two or more spells during their turn, it becomes day.
Shady Traveler // Stalking Predator
Day and night are designations that the game itself can have. The game starts as neither. Once the game becomes day (or less commonly, night), the game will be exactly one of them—day or night—going back and forth for the rest of the game.
If it is night, permanents with daybound that enter the battlefield without being cast will enter with their nightbound faces up.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Lie Setiawan
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
