Complex sentence: Greg takes the chance to get books from a horror series, "Spineticklers", which makes Susan more unhappy: she wanted Greg to join advanced classes, but he showed a poor attitude and arrogance so to deliberately fail the entrance exam.
Split into simpler sentences: Greg takes the chance to get books from a horror series, "Spineticklers", which makes Susan more unhappy. She wanted Greg to join advanced classes, but he showed a poor attitude and arrogance so to deliberately fail the entrance exam.