Encounters: Cormyrean Marshes - The Marsh of Tun

Dragon, Black Old (Skurge) (CR 15)

Huge Dragon (Water)
Alignment: Always Chaotic Evil
Initiative: +0; Senses: blindsense 60 ft., darkvision120 ft., low-light vision, and keen senses
Languages: Draconic

AC: 32 (-2 size, +24 natural), touch 8, flat-footed 32
Hit Dice: 25d12+125 (287 hp); DR: DR 10/magic
Fort +19, Ref +14, Will +16

Speed: 60 ft., fly 150 ft., (poor), swim 60 ft.
Space: 15 ft./10 ft. (15 ft. with bite)
Base Attack +25; Grapple +42
Attack: 1 Bite +32, 2 claws +27, 2 wings +27, 1 Tail Slap +27, 1 crush +27 melee; Breath +32 ranged
Damage: 1 bite 2d8+9, 2 claws 2d6+4, 2 wings 1d8+4, 1 tail slap 2d6+13, 1 crush 2d8+13, Breath weapon 16d4 (27)
Special Attacks: Breath weapon, fear (DC 27), SR 22

Abilities: Str 29, Dex 10, Con 21, Int 14, Wis 15, Cha 14
Special Qualities: Acid immunity, water breathing, Darkness, Corrupt water; Plant growth CL 7th
Feats: #Feats: 9
Skills: Skill points: 56
Advancement: 26-27 HD (Huge)

Climate/Terrain: Any marsh and underground
Organization: solitary, pair, or family (1-2 and 2-5 offspring)
Treasure: Double Standard

Source: Monster Manual

Breath Weapon (Su): A black dragon has one type of breath weapon, a line of acid. Using a breath weapon is a standard action. Once a dragon breathes, it can't breathe again until 1d4 rounds later. A blast from a breath weapon always starts at the dragon's mouth and extends in a direction of the dragon's choice. The black dragon's breath weapon deals 16d4 acid damage. Creatures caught in the area can attempt Reflex saves (DC 27) to take half damage.

Water Breathing (Ex): The dragon can breathe underwater indefinitely and can freely use its breath weapon, spells, and other abilities while submerged.

Corrupt Water (Sp): Once per day the dragon can stagnate 10 cubic feet of water, making it become still, foul, and unable to support animal life. The ability spoils liquids containing water. Magic items (such as potions) and items in a creature's possession must succeed at a Will save (DC 24) or become fouled.

Other Spell-Like Abilities: 3/day - darkness (radius 80 feet) ; 1/day - plant growth.

Faerûnian Random Encounters by Region and Locale