Pandora is a servant of Medusa that first appeared in the original Kid Icarus as one of the game's bosses. She is the goddess of calamity and has the appearance of a large, amorphous blob of energy.
Kid Icarus: Uprising
In Kid Icarus: Uprising, Pit journeys to Pandora's home, the Labyrinth of Deceit, in order to destroy the Mirror of Truth she possesses to prevent Medusa from using it to increase her army's ranks. At the end of the labyrinth, he manages to defeat her, and then smashes the mirror. However, in doing so, he falls for Pandora's trap. By smashing the mirror, Pit creates a dark duplicate of himself; Dark Pit.
Pandora at first gloats, believing that she's acquired a powerful ally, but is caught off guard when Dark Pit attacks her. Because the mirror had been cracked before Pit smashed it, Pandora is unable to control the duplicate. She is defeated when both Pits attack her in tandem. Following her defeat, Dark Pit steals Pandora's power for himself and acquires the ability to fly without any time limit.
Late in the game, Dark Pit arrives at a renewal spring in order to use the water's power to restore Pit's health. It is at this point that Pandora makes a move to return, and her remaining essence escapes Dark Pit before submerging in the water. Restored to full health, she attempts to get revenge on Dark Pit, but is overpowered once again. Unwilling to accept defeat, she returns to the spring and bathes in it a second time, allowing its power to restore her to her youth of ages ago, when she still had a body. Fully revitalized in her amazonian body, she flaunts her beauty to the disgust of Palutena and Viridi before continuing her fight with Dark Pit. However, even with a body, her renewed strength isn't enough, and she's defeated once again.
Pandora's name and her status as the goddess of calamity are references to the Pandora of Greek myth. In the legend, Pandora was a mortal woman that unwittingly unleashed calamity when she opened a box containing all of the world's evils.