The Madragon is an boss from Grandia. It is encountered at the peak of the Volcano. Madragon appears in two parts, but it's HP depletes as one. Madragon has the ability to cast Flame Breath, Blast Breath, Burn!, Healer and Howlslash.
The head and the body share the same health, but the head has the most attacks. Therefore, focus on attacking and canceling the head throughout the battle. The body will occasionally attack with its claws if there are characters directly in front of the beast. The head has two strong attacks: Flame Breath, which can only target those in front of the monster and Howlslash, which attacks all party members for heavy Wind damage.
Gadwin will actually be the weakest here since he only can use Earth, Fire and Explosion spells. Don't bother using Dragon Cut in this battle, instead use Flying Dragon Cut, combos, and critical attacks with him. You may want to strictly have Gadwin use critical attacks if you feel it'll better benefit the party's survival. The other option is to have Gadwin buff the party with Diggin' and WOW!, then have the others attack.
If Justin has learned Ice Slash it can really hurt the boss, so use it if you have it available. In addition, equipping Justin with the Raincloud Staff, Sue with either the Raincloud Staff or Hail Bow and Feena with the Azure Knife will make battles with the Madragon much easier.