Mars is a planet that first appears in the animated short. In it, Pen (later changed to Finn) gets frozen by one of Ice King's frozen lightning bolts, and his mind gets transported back in time and to Mars by Abraham Lincoln, who gives him the courage to believe in himself. Earth appears normal in the background, which is explained by the fact that this scene takes place "back in time." The planet also makes a few appearances in the series Adventure Time. In "Too Young," Peppermint Butler...
