I found this fight fairly straight forward and quite a bit too easy on normal settings using level 21 characters. Two of my guys were set to be total brutes hack 'en slashers. The archer knew the minor hp recover skill and could summon ice and spiders. I used the mage to also summon other elemental placing them in the front line. The archer would use some charm arrows on the dragons summons. I had to heal Astroge once. My brutes laid it into the dragon hard and the archer used some scrolls and silver tipped arrows to weaken him. When every one was healed up the mage would drop a poisoned rock from the sky or a small fire ball using the archer's silver tips would help as well. Air seemed useless against the dragon but once weakened he could be stunned but may end up wasting your ap if trying to stun him soul sap seemed to help as well.
Weapon: Fatal Sharp ornate Scythe of the Fire Band Slashing 155-393 Fire 46-117 Tenebrium 46-117 Critical Damage x2.0 Critical chance 5% Strength +2 Dexterity +2
Weapon: Concrete Mystical Earth Staff of the Colossal Fire 5-13 Critical Damage x1.5 Strength +2 Dexterity +2 Intelligence +3 Constitution +3 HP +101 10% chance to set petrified 15% Chance set Mute