Kefka ending the world remains the most memorable moment to me. Up to that point the villain never really won in the conflict being told. They'd always come close and then lose, but not Kefka. He managed to succeed in his plans to bring ruin to the world and changed the whole landscape of the game and brought on themes of depression and suicide I never would've thought could be told maturely in a children's video game. It's actually quite beautiful.