- Rock War I was when Giegue did this 1000 years ago; when he traveled back in time and the Chosen 4 followed him as robots.
The second attempt has you using your powers to directly kill Giegue before he can become Giygas, either through cheating or item manipulation. Reality can't take it. Everyone turns into cows.
Third attempt has you remembering MOTHER, and giving Niiue the powers of the Song. But this crushes Giygas completely, which results in a time paradox. The Apple had Observed Giygas rising, Observed the Chosen Four beating him. The time paradox is a good thing in that it convinces the Apple of Enlightenment to ease up on interpreting the Prophecy.
So restart. Fourth attempt. This time, the party pulls Giegue out of Giygas. With YOU it can be done. And even though this is the happiest of endings possible in the timeline so far, YOU try one more time.
One last try for a happy ending. It requires having Alinivar soften the Song through Harmony. Niiue pulls Giegue temporarily out of Insanity. He has the power of Giygas, but hell be consumed by it soon enough. BUT he and Niiue want to try something. Something they both want.
This creates a new timeline where Giygas was never created. Granted, the old timeline still exists, and it will take something special to erase Giygas from all timelines.
But what did they do to create a new timeline that didnt crash? They went back in time to before the Apple Observed the prophecy, and either saved Maria from being turned into Queen Mary in Magicant; or else used PSI power to give her a new body in the physical world. Child-Giegue gets his Mother; preventing Giygas from ever existing, and the remaining party members live in peace in the new world. Niiue asks You to go and help Ness because the timeline that Zarbol went to is still in danger.
So were left with 2 timelines. Severance taking place in the old timeline, and Good taking place in a new timeline. And YOU and the Chosen Four clean up whats left.