In Level 4, you are forced to jump through a magic mirror, which creates a "Shadow" doppelgänger of yourself. This shadow hinders your progress throughout the game, but since you share a life force, you cannot kill it without killing yourself.
The story of the original is a classic "save the princess" race against time set in medieval Persia. The Plot: An Hour to Live
Eventually, you must merge back with your shadow to cross an invisible bridge and reach the tower for a final sword duel with Jaffar himself. How to Play Today (PC)
To save her, you must navigate a 12-level labyrinthine dungeon and palace within exactly of real time.