It is recommended to start the fight with the Blade Dragon during the Waxing Moon to reduce the damage from his elemental attacks. The Waxing Moon lowers damage from Black Magic, including the party's own spells, but this will not matter because the boss still takes great damage when it is hit with the element it is weak against. Whenever hit with elemental magic, the Blade Dragon changes its elemental weakness with Barrier Shift, which will be either Fire, Ice, or Lightning. If it is attacked with non-elemental magic, it will retaliate by using Venom Breath, which hits Palom and Leonora for heavy damage and inflicts Sap for a short time. He will then use Leech and restore one third of his current HP, which at the start of the battle can be over 4000HP. In order to discover the Blade Dragon's weakness, the player must observe which elemental attacks it uses. For example, if the Blade Dragon casts Fira and Thundara, it is vulnerable to Ice. If the party happens to hit it with one of the elemental attacks it is not weak against, it will be healed by the damage and counterattack with that same element. Victory is ensured if the player examines his attacks and uses the right magic with Palom, while keeping the party alive with Leonora's White Magic. While waiting to see what the Blade Dragon's weakness is, it will also be highly beneficial to have Leonora cast Shell on the party to boost Magic Defense. It is also a good idea to use a Spider's Silk or cast Slow on him. He will counterattack it but it will also make healing much easier because he attacks quickly.
When Palom and Leonora are at a high level, they can use their Band ability, Particle Bomb, to take off the last 6000 or so of the Blade Dragon's HP.