Day and night are special themes of the game A Koopa's Revenge II. The game switches between each theme every time the player either loses a live or finishes a level. Differences include:
In 2-4, the enemy is the sun if it's day and the moon if it's night.
In 3-2, the block at the beginning of the level contains a Purple Shell power-up if it's day, but multiple coins if it's night.