Medusa

Medusa, was the co-ruler of the kingdom Angel Land, Palutena is the other ruler, Medusa hated mortals and used the power of darkness to destroy their crops and turn them into stone. Palutena then finds out about Medusa's doings and turns her into a hideous monter and banishes her to the underworld.

Revenge
Medusa did not want to stay with her arms crossed, she decided to get back at Palutena. So Medusa joined forces with evil spirits, and monsters. Luckily Medusa's army defeated Palutena's, then she banishes Palutena into a cage and gives the three-sacred treasures to her most trusted monsters.

Medusa did not think Pit could be such a challenge, since the poor little angel was stuck in the underworld. Palutena, with her remaining power, helped Pit out of the underworld and sends him a magical bow. Pit gains the three treasures and then defeats Medusa.

Other Appearances
It's unknown if Medusa can return to the possible future sequel since Medusa did not appear in the second title. However Medusa was requested, in the polls, to appear in Smash Brothers Brawl, it might be very possible she appears in the game.