Complex sentence: The Ghostly Trio soon discover Casper's good deeds and abduct him, which unfortunately ruins Chris's opportunity to have Tim meet Casper as Tim does not believe Chris, and instead leaves to visit the mayor.
Split into simpler sentences: The Ghostly Trio soon discover Casper's good deeds and abduct him. Unfortunately, this ruins Chris's opportunity to have Tim meet Casper as Tim does not believe Chris, and instead leaves to visit the mayor.