Dragon, Black Ancient (CR 18)
AC: 38 (-2 size, +30 natural), touch 8, flat-footed 38
Hit Dice: 31d12+186 (387 hp); DR: 15/magic
Fort +23, Ref +17, Will +20
Speed: 60 ft., fly 150 ft., (poor), swim 60 ft.
Space: 15 ft./10 ft. (15 ft. with bite)
Base Attack +31; Grapple +50
Attack: 1 Bite +40, 2 claws +35, 2 wings +35, 1 Tail Slap +35, 1 crush +35 melee; Breath +40 ranged
Damage: 1 bite 2d8+11, 2 claws 2d6+5, 2 wings 1d8+5, 1 tail slap 2d6+16, 1 crush 2d8+16, Breath weapon 20d4 (31)
Special Attacks/Actions: Breath weapon, fear (DC 35), SR 25
Abilities: Str 33, Dex 10, Con 23, Int 16, Wis 17, Cha 16
Special Qualities: Acid immunity, water breathing, Darkness, Corrupt water; Plant growth; Insect plague CL 11th
Feats: #Feats: 11
Skills: Skill points: 99
Advancement: 32-33 HD (Gargantuan)
Climate/Terrain: Any marsh and underground
Organization: solitary, pair, or family (1-2 and 2-5 offspring)
Treasure/Possessions: Double Standard
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 20d4 acid damage. Creatures caught in the area can attempt Reflex saves (31) 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 28) or become fouled.
Other Spell-Like Abilities: 3/day - darkness (radius 100 feet) and insect plague; 1/day - plant growth.
This subtype usually is used for elementals and outsiders with a connection to the Elemental Plane of Water. Creatures with the water subtype always have swim speeds and can move in water without making Swim checks. A water creature can breathe underwater and usually can breathe air as well.