In an effort to win the war, the Wizard of Oz used a special key to split Charlie into her dark self and her good self. Dark Charlie won in Oz, as intended, but her dark persona ran away to avenge her parents in the real world.
Charlie proves to be violent and goes as far as torturing people and slashing the Impala's tire to keep the Winchesters from following her. However, it turns out there are two Charlie's: Good Charlie and Dark Charlie.
