Adventure Time can throw in a song reference for fun, but it can also throw in a song reference that heavily foreshadows events to come. “Crossover” does the latter and packs an enormous amount of foreshadowing to the episode “Flute Spell.” Both episodes were written and storyboarded by the team of Jesse Moynihan and Sam Alden, so the chance of this being a mere coincidence that worked out phenomenally is slim to none.

Check out my review of "Flute Spell":
   • Adventure Time Review: S7E25 - Flute ...  

Music:
“I’m Just Your Problem” (Instrumental Arrangement) by John Q4 (John Hernández). Original song composed by Rebecca Sugar and Tim Kiefer.

Island Song - Instrumental (Adventure Time Ending Theme) by Ashley Eriksson.