Chrono Trigger/The Guru on Mt. Woe

Chrono Trigger > Chapter 20: The Guru on Mt. Woe (12,000 B.C. second time)

Challenging Lavos
If you go back and challenge Lavos at this point, you should get The Prophet Ending. There will be a few scenes involving "the Prophet" from this period and particularly nice speech from him, hinting that he would have gotten the chance to do what he wanted without your interference.

Continue to Chapter 21: What Lies Beyond? (12,000 B.C. second time)