4. Simon And Marceline's Story
Out of all my questions, this is the one actually appears to be getting slowly answered. Several episodes have explored some of Marceline and Simon's (Ice King) history, such as "I Remember You" where it's revealed a then stable Simon helped lost, young Marceline survive during the Mushroom War. Simon even gave her the treasured Hambo to comfort her. Limited parts of their past have been cleared up, but how they separated, how Marceline returned to her family, and the complete details of Simons transformation into the Ice King still remain shrouded in mystery. For me, this history of Simon and Marcy is one of the most interesting aspects of the show. "I Remember You" is a must watch episode for any Adventure Time fan, its emotion and plot is top notch, and I can't wait for more history of this friendship to reveal itself.