Complex sentence: Seeing the proven existance of Unicron as an opportunity to start a revolution and attempting to join the Decepticons, they met Shockwave, who offered to bring Zetimus to the Decepticon leader, Megatronus.
Split into simpler sentences: Seeing the proven existance of Unicron as an opportunity to start a revolution, he attempted to join the Decepticons. He met Shockwave, who offered to bring Zetimus to the Decepticon leader, Megatronus.