Adventure Time | Pilot | Nickelodeon/Cartoon Network

The short focuses on a boy named Pen (later renamed Finn in the television series) and his best friend, a shapeshifting dog named Jake. One day, Lady Rainicorn, a unicorn-like creature, flies past them in tears; Pen and Jake follow her to an icy domain, where they discover that the Ice King has kidnapped Lady Rainicorn's owner, Princess Bubblegum, in the hope of marrying her.