It's Ice kings Birthday,
when everybody has arrived Finn & Jake forgot to get a birthday present for Ice king. So Jake decides to take Ice king over to Prismo's, to make his wish. The wish is Ice king tells Prismo his wish. For his Fionna & Cake fanfic and all the characters to come to life. By making this happen Ice king reads the fanfic's and reads the other Fionna & Cake fanfic's that others made for him. So Prismo can visualize the characters, and background.
.....,
I just thought of something in the 8th episode season 5, mystery dungeon, on Adventure Time.
When the ice king was trying to make his Fionna & cake fanfiction come to life. But failed.
And the episode of bad little boy
Nearly at the end, Ice king says...
to the Fionna & Cake ice sculptors that he made.
But what if ice king told Prismo about his fanfiction. Including what others made, in the 3 episodes. And made a wish for everybody in the Fionna & Cake to come to life in reality.