Onyx Dragon [Mystara]

At 120 feet or more an onyx dragon looks just like a black dragon, unless the sun is bright, when its gleaming scales stand out. Up close, its glossy, jewel-like scales sparkle, and in full sunlight its deep black hide flashes like a thousand mirrors. It speaks its own language and the gem dragon tongue, plus a little common or whatever humanoid language is spoken nearby.

Not especially bright, it is cunning and quiet on the hunt. Its breath is a filthy black cloud of acid that first acts like a black dragon's corrosive stream, halved with a save vs. breath weapon. Anyone who fails that save must save vs. spell or be engulfed by darkness, 15-foot radius, that follows him wherever he goes. It lasts a number of rounds equal to the dragon's Hit Dice unless a light spell counters it or dispel magic removes it (the dragon's age category is the caster level to overcome). It otherwise works like normal darkness, but the dragon sees through it easily. A successful second save leaves the darkness in place but not attached to the victim, who can walk out of it. Onyx dragons sometimes breathe darkness before a fight to hide and gain surprise.

They live in swamps, bogs and fens from the tropics to the cooler edges of the temperate lands, preferring dark, heavily shaded places such as wooded bogs, where their glittering scales are less likely to alert prey.

They hunt the largest animals around, such as alligators, herons, manatees and moose. They will eat humanoids but are smart enough to know adventurers may cost more than they are worth as a meal. They value treasure, especially dark, glossy gems, but tend to own less of it than other dragons.