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Lemonjon first appears in the episode "All Your Fault." He is a giant Lemon Person created by the Earls of Lemongrab who is so large that his various organs exist in separate rooms within Lemon Castle. His head appears within the castle itself as a giant living wall with a Lemongrab-esque face.
When Finn and Jake first encounter Lemonjon, he is seen only as a large, rectangular, yellow face. Once he stands up, he reveals that he is a giant, yellow lemon person. He seems to have two noses. He also has fluffy yellow "hair" on the top of his head, divided into three parts.
- In the episode "All Your Fault", he is voiced by Justin Roiland. In the game, he is mute.
- Lemonjon is the first non-playable character to be a renovations project, and in brick form.
- Similar to the episode he appeared in, Lemonjon will grab a stone with his mouth and smash the wall which leads to the dungeon holding the two Lemongrabs.