Story Based Trophy
Yu Yevon is the final boss of the main storyline, and the fight it self is not hard. Upon entering you will automatically start of with auto-life on all characters making it impossible to lose. Bring out any characters who have Doublecast and a high magic, and waste away on him. He will counter this by using Curaga on him so at least half of your attack will affect him, you can counter this if you have learned Zombie Attack as this will cause him to hurt himself then cure himself. He will also occasionally cast Gravija on all members (including himself for 9999 damage) but do not worry about healing as if you die you will be constantly revived from auto-life.
Upon completion you will beat the game and witness a long cutscene followed by the credits.