Ep 5. Return to the Nightosphere/Daddy's Little Monster

Finn goes on a journey to the Nightosphere with Marceline to retrieve her father, released from the Nightosphere years ago by Marceline herself. Upon arrival, they quickly learn that Marceline's father, Hunson Abadeer, has taken over the Nightosphere and become a cruel ruler. After unsuccessfully trying to reason with him, Finn and Marceline team up with a demon named Peppermint Butler, who has a secret connection to Hunson.

Meanwhile, back in the Land of Ooo, Princess Bubblegum discovers that she mistakenly created a monster while attempting to create a clone of herself. The monster, who she dubs "Lemongrab 2," is a child-like creature who is both frightened and fascinated by the world around him. Bubblegum attempts to raise Lemongrab 2 with kindness and compassion, but her efforts are challenged when Lemongrab 2's more aggressive instincts begin to emerge.

As the two storylines progress, Finn and Marceline face numerous obstacles in their quest to defeat Hunson and restore order to the Nightosphere, while Princess Bubblegum struggles to understand and connect with her newly-created monster. The episode culminates in a climactic battle in the Nightosphere, with Finn and Marceline fighting against Hunson and his army of demons, and Bubblegum attempting to reach Lemongrab 2 before it's too late.

Overall, "Return to the Nightosphere/Daddy's Little Monster" is an action-packed episode that also explores themes of family, power, and the consequences of scientific experimentation. With a thrilling plot, lovable characters, and a healthy dose of humor, it is a must-see for Adventure Time fans.