Complex sentence: Sunny's band decided to lock up the door and never speak of it again, and it was forgotten until Li'l D and the others defeated it by turning it into a huge sloppy joe and selling it.
Split into simpler sentences: Sunny's band decided to lock up the door and never speak of it again. It was never seen again until Lil' D and the gang defeated it by turning it into a huge sloppy joe and selling it.