Hissing green acid drips from the fanged maw of this black-scaled, horned dragon.
5e SRD
Green-skinned dragons so dark they appear black, especially in water
Swamp dragons have green skin so dark as to appear to be black, especially in uncertain light or while wet. They often choose to hide underwater, leaving only part of the head above the waterline, and leap up suddenly when prey comes within 100' (surprising on a roll of 1-4 on 1d6 in this case).
Though swamp dragons are more cruel than ice dragons, they are still motivated mostly by the urge to live, breed and collect valuable items.
Swamp dragons are immune to all forms of acid. A swamp dragon may hold its breath up to three turns while lying in wait underwater.
Basic Fantasy Role-Playing Game
A proud, ancient race of gigantic, carnivorous, winged reptiles. There are many subspecies of dragon, many of which are distinguished by the colour of their scales. All dragons are egg-layers and hoard treasure in their lairs, far from areas of human civilisation.
OSE
Fearsome dragons that spew corrosive venom, found in swamps, marshes and deep, dark caves
Viking champions such as Ragnar Lodbrok and Sigurd the Volsung fought fearsome dragons that spewed a corrosive venom, deadly to the touch. These dragons are the deadly black dragons. Black dragons are found mostly in swamps, marshes and deep, dark caves.
Black dragons only occasionally (30%) are known to speak, only rarely (10%) cast magic, but often (50%) will be found asleep. If the dragon is asleep, there is a 1 in 6 chance that it will awaken in the presence of adventurers. Dragons also sometimes feign sleep.
If a black dragon can cast spells, it will gain spells as a magic user of a level equal to one half of its age category. So, an ancient black dragon casts as a 4th level magic user.
OSRIC