- They're black, obviously. 
- People thought they were common because the darkness dragon, a common breed, looks very simular to them.
- They can enter the body of any animal (including humans) and control them.
- Seeing a black dragon not in an animal is believed to be bad luck.
- Black dragons hated white dragons.
- Black dragons are vile, evil-tempered and obsessed with death.
- They find comfort in the sickening-sweet aroma of a drowned rotting carcass.
They have membrane wings.
The size of each wing is equal to the size of the body.