Deep dragons are little known on the surface world. They are the hunters of the Underdark. Cunning and patient, they place their survival, followed by their joy of hunting, above all else. Deep dragons carefully amass and hide treasure in various caches, guarded with traps and magic. They are able to use most magical items.
Deep dragons are an iridescent maroon when they hatch, soft-scaled, and unable to change form. They keep to their birth-lair until they have mastered both of their other forms-a giant winged worm or snake and a human (or drow) form.
Deep dragons burrow and fight with powerful, stone-rending claws. They love to fight and hunt prey through the lightless caverns of the Underdark, employing their various forms. In snake form, they are AC 6, MV 9, Fl 4(D), Sw 11, losing claw attacks, but gaining a constriction attack (attack roll required, inflicts 3d8 points of damage per round, hampers movement, spellcasting, and causes -1 on attack rolls and a 1-point AC penalty).
In human form, a deep dragon is AC 10, MV 12, Sw 12, and causes damage by spell or weapon type. Armor can be worn, but it is always destroyed (inflicting 2d4 points of damage to the dragon) in any transformation of shape. A deep dragon can alter its features to resemble any humanoid of roughly human size.. It is 66% likely to copy a specific being well enough to be mistaken for the actual creature.
A deep dragon's breath weapon is a cone of flesh-corrosive gas 50 feet long, 40 feet wide, ad 30 feet high. Creatures in the cloud can save vs. breath weapon for half damage (if they have dry, exposed skin, they save against the flesh-eating gas at -2). Cloth, metal, and wood are not affected. Leather is treated as dry, exposed skin.
Deep dragons cast spells at 9th level, adjusted by their combat modifiers. They are born with infravision, true seeing, and unerring detect magic abilities, and immunities to charm, sleep, and hold magic. Deep dragons are immune to extremes of heat and cold (-3 on each die of damage taken, to a minimum of 1 hp per die).
As deep dragons age, they gain the following additional powers:
Very young: assume snakeform 3 times/day
Young: assume "human" form 3 times/day
Juvenile: one more form change/day (each), regen. 1d4 hp/turn
Adult: regenerate 1d4 hp/6 rounds; free action at will
Old: transmute rock to mud and telekinesis 3 times/day
Very old: move earth 3 times/day
Venerable: passwall and disintegrate 2 times/day
Wyrm: one additional use/day of powers gained since Old age; stone shape 2 times/day, tongues once/day
Great wyrm repulsion 3 times/day, affecting all except dragons. One additional use/day of stone shape and tongues
Deep dragons roam the Underdark and are great explorers. Most often deep dragons are found in well-defended lairs in the Underdark. They often use their powers to reach caverns inaccessible to most creatures. Deep dragons often work with drow.
Deep dragons have been known to eat almost anything, but they particularly prize the flesh of clams, fish, kuo-toa, and aboleth. They view cloakers and mind flayers as dangerous rivals in the Underdark. Deep dragons avoid confrontations with other dragons and never fight or steal from others of their own kind.