Mastery Level indicates how well you have mastered a certain room. You can learn the room's Mastery Level by checking the number of stars in the room window.

The higher the Mastery Level, the higher the reward for successfully exploring a room. The change in Mastery Level can affect the amount of energy required for exploring, as well as the number of required items.

At higher levels of difficulty (Mastery Levels), objects in a room can be presented in a different form (different color, different shape).