List of episodes/Season 4

Season 4 premiered on April 2, 2012. Episode titles were posted on the Frederator Blog in March 2012.

Writing of the season had started by May 2011. The season saw the premiere of the 100th episode of the series, "The Hard Easy" (previously titled "Prince Huge"). Adam Muto reported that characters not seen since the earlier seasons would return, with The Earl of Lemongrab, Magic Man, the Lich, Hunson Abadeer and Neptr being confirmed to return. Prior to the season's airing, Adam Muto said that Marceline's backstory would be explored further, and Jeremy Shada also mentioned that Marceline and Ice King would sing together,, which took place in the episode "I Remember You." The season featured guest voices by Donald Faison, George Takei, Erik Estrada, Andy Milonakis, Emo Phillips, Bobcat Goldthwait and Susie Essman. The season featured one complete two-parter ("Return to the Nightosphere" and "Daddy's Little Monster"), however the season's introductory episode was a continuation of the season 3 finale, and the season 4 finale continued into season 5's two-part opening episode.