Complex sentence: The player can start with any level that who has already beaten from the main game, and add new objects with new properties for the game that significantly vary from the normal behavior, such as having a bear able to eat a plane.
Split into simpler sentences: The player can start with any level that they have already beaten from the main game, and add new objects with new game properties. These new properties can vary significantly from the normal behavior, such as having a bear able to eat a plane.