Make sure the dragon is always on top of your fighter with the lowest AC. Make sure you use whirlwind or greater whirlwind, and be sure to dispel his proctection from magical weapons. Sometimes dragons use haste and this is definitely not a good thing. (30 damage 5 attacks per round.) Breach will get rid of this as well. Have your priests ready to cast heal, when hp gets low. He will fall eventually. (Have some potions of superior healing ready in case the priest gets nailed.)
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