Astral dragon

Astral dragons were rare and powerful planar dragons native to the Astral Plane.

Abilities
Astral dragons could see through the blur of the Astral Plane for up to 10 miles (16 kilometers), and could plane shift at will. They were able to fly on the Prime Material Plane thanks to an organ in the head, although they were not easily able to walk under the effect of gravity.

Combat
In battle against creatures not native to the Astral Plane, the astral dragon would prioritize attacking spellcasters, since they might be responsible for keeping their companions in the Astral Plane, so killing them would defeat the entire group.

Although an astral dragon had no psionic abilities, it could sense psionic abilities in others, up to around 240 feet (73 meters).

Birth and development
Every few hundred years a female astral dragon could lay one egg, which was about in diameter and the same color as the rest of the Astral Plane, making it difficult to see. This egg grew, over many years, until it was in diameter, at which point a hole opened at one end. The egg itself became the hatchling's lair, and it continued to grow to a maximum of around in diameter, at which time it was very thin (although still strong).

A young astral dragon used the egg for storing treasure, much like a regular lair, and established a mental link back to the egg, to find it later. Once adulthood was reached, the egg was abandoned in favor of a larger lair, and these eggs were often taken over by other species.

Younger astral dragons spent more time on the Prime Material Plane than their adult counterparts, and the older the dragon became, the more time they spent on their native Astral Plane.

Astral dragons only grew to around in length ordinarily, but that changed when two of them mated, at which the pair increased in power and size (growing to  in length), and a magical chain appeared which bound the two together. The chain could extend up to and said to be a sign of their devotion to one another. Astral dragons considered this chain a blessing. Additionally, mated astral dragons made huge palace-lairs which they rarely left, but were close to demipowers in might in their domains. To gather information, they would send out kodragons instead.

Diet
The astral dragon did not require very much food, but they did enjoy eating, preferring githyanki where possible.

Disease
Some astral dragons contracted a disease known as astralomitis, which inhibited their ability to travel the planes, and was more common amongst astral dragons who switched between planes frequently. If a dragon was on a non-native plane when struck by this disease, it was unable to return, and there was a chance that insanity would ensue. It lost the ability to cast any spells in this state, but ferociously attacked any creatures nearby. This state could last for up to five days, and resulted in the death of the dragon. If it could return to the Astral Plane by this time, the insanity slowly diminished, but it was left unable to switch planes. The disease had no known cure except for a wish spell.

Treasure
Astral dragons, like some other dragons, had a desire for treasure, and sought to acquire it by traveling the planes. A favorite target was githyanki, since they tended to have magical, gem-encrusted armor, but an astral dragon also enjoyed treasure acquired from astral travelers. Magical treasure recovered from an astral dragon's lair on the Astral Plane appeared normal unless it was returned to the Prime Material Plane.