"Daddys Little Monster" solves many of the unanswered questions from the previous episode, "Return to the Nightosphere", explaining how Finn and Jake arrived to that hellish place and what happened to Marceline. Oh, and there is also a very funny (albeit a bit gross) revelation the bananas from the Nightosphere.
Additionally, this episode shows the weird, twisted relationship that Hunson Abadeer has with her daughter, making clear that (from his perspective, at least) turning her into a monstrous being and traumatizing Finn in the process (look at his reaction at the end of the episode) was a genuine gesture of love. Considering that Hunson Abadeer is a demon, that shouldn't surprise me.
Additionally, this episode shows the weird, twisted relationship that Hunson Abadeer has with her daughter, making clear that (from his perspective, at least) turning her into a monstrous being and traumatizing Finn in the process (look at his reaction at the end of the episode) was a genuine gesture of love. Considering that Hunson Abadeer is a demon, that shouldn't surprise me.