Complex sentence: He first appears in "Treehouse of Horror VI", when Homer tries to get a colossal donut, but there is no such thing, so he steals the real one that Lard Lad holds.
Split into simpler sentences: He first appears in Treehouse of Horror VI when Homer tries to get a colossal donut, but there is no such thing. Then Homer steals the real one that Lard Lad holds.