If, after defeating a boss, you use your Teleport spell to exit the room before the door barriers vanish, the game will not actually consider the boss to be defeated, allowing you to return and refight that boss on the same day. This can be useful for grinding Prince/ss Points and farming drops from a particular boss. Simply wait for the boss's death animation to finish and the game to produce its drops and give you your PP, and then teleport out. The drops will still be in the room when you come back! Be aware that this glitch cannot be used in the Sharance Maze, due to the randomly generated nature of the place.