Dragons can teach you an appropriate destructive spell, if you befriend them: acid rain, lightning bolt, fire ball and snow storm (3rd circle) all deal 6d6 damage of the appropriate kind, save vs. spells for half. Poison gas (5th circle) will kill any creature with up to 4 HD unless they save vs. poison. Those that save and any creature above 4 HD simply suffer 1 damage/round.
Dragons are the most powerful guardian spirits there are. Any majestic river, mountain or forest will have a dragon. Dragons are forces of chaos: they oppose civilization and will try to destroy settlements, sometimes making their lair in the ruins of once rich and powerful towns and cities.
All dragons are intelligent and speak the languages of many ancient empires and the languages of any people currently living in the area. They have seen it all. Their heart is bent on destruction. Collecting the treasures of the cities they sacked is their way of preventing a reconstruction.
Dragons can use dragon breath (3×/day): a cone about 100 ft. of ice, acid, poisonous gas, lightning bolts or fire, depending on the color of the dragon. Take as much damage as the dragon still has hit points left. Save vs. dragon breath for half damage. Dragons are themselves immune to such effects and even if the target of a spell with such an effect (lightning bolt, fire ball, snow storm), the dragon takes only half damage and saves vs. spells for quarter damage. In addition to that, they are immune to non-magic weapons. All dragons can fly.
White: HD 6 AC 3 1d4/1d4/2d8 F6 ML 8 MV 24 XP 1070; ice
Black: HD 7 AC 2 1d6/1d6/2d10 F7 ML 8 MV 24 XP 1490; acid
Green: HD 8 AC 1 1d6/1d6/2d8 F8 ML 9 MV 24 XP 2060; poison
Blue: HD 9 AC 0 1d8/1d8/3d10 F9 ML 9 MV 24 XP 3100; lightning
Red: HD 10 AC -1 1d8/1d8/4d8 F10 ML 10 MV 24 XP 3100; fire
Treasure: Todo. Immense. Could be several times what a dwarven city has, for example.
Terrain: caves, deserts, forests, jungles, mountains, ruins, swamps.