Complex sentence: When Diana attempts to kill Ares with the Godkiller sword, he destroys it, then reveals Diana to be the "Godkiller", as the daughter of Zeus and Hippolyta, but he fails to persuade her to help him destroy mankind to restore paradise on Earth.
Split into simpler sentences: When Diana attempts to kill Ares with the "Godkiller" sword he destroys it, then reveals Diana to be the "Godkiller", as the daughter of Zeus and Hippolyta. He fails to persuade Diana to help him destroy mankind to restore paradise on Earth.