The Moonlight Butterfly is a boss that does no physical damage whatsoever, so stack up on magic defense (Crest Shield is one good item). This boss, for most of the fight, is airborne, so melee characters won't get a good chance to attack it until a little later on in the fight. Its attacks can be simple to dodge, once you get used to them; one helpful tip is to wear heavier armor so you roll on the ground longer. There are only a handful of attacks that the Moonlight Butterfly does. It will fire off some slow moving projectiles that home in on you; simply roll when it gets close. It will also fire some fast moving needle-like projectiles; just keep moving with your shield up (if you have a shield with good magic defense) to hopefully dodge this attack. It will also fire a beam that goes from one end of the walkway to the other side; it doesn't go from one extreme end to the other, so a well-timed roll should be enough. Sometimes, when it switches from one side of the bridge to the other, it will release a bomb-like attack on the bridge, so hopefully it's not close to you when it drops the attack. Once it does some attacks from the air, it will eventually land on the bridge. This is your chance to just go wild with your attacks, as it won't attack you at all while it's on the bridge. Once you see the boss start glowing, that's your cue to stop attacking and get out of the way, as the boss will do a little pulse attack and then take to the air again. It should take probably 2 rounds before you take this boss down.