Dragon

Most dragons had six limbs - two forelegs or arms, two hind legs, and two wings. Their bodies were serpentine: long, thin, and flexible. The body was covered in hard keratin scales, which came in a variety of colours based on genetics and environment. Dragons were able to rotate their forelegs outwards and in complete circles, in a manner similar to primates. They had hand-like paws with needle-like claws, which could not be retracted. Most wings had membrane, but some dragons had feathered wings. Dragons that did not have much need for flight, such as Nether dragons, had small, vestigial wings. Dragons had streamlined, crocodile-like heads with horns, two rows of teeth, and unforked tongues; some dragons had fangs that were so long they were prominent even when the mouth was closed. Dragons usually had either a row of horn protrusions or a mane running the length of their spine.

The only known living dragon - the Ender Dragon - is confirmed female.
Dragons were oviparous, laying large eggs with hard shells. Upon finding a mate, they would engage in an elaborate synchronized flight dance. If the prospective mate could not do the dance to the other's liking, they would be rejected. After successfully doing the dance, the dragons would mate and then part ways. They were known to mate with dragons of the same sex as often as they would with the opposite.

They were a highly adaptable species that made many biomes their homes. Dragons could be found in all three dimensions -- lithe and athletic Overworld dragons; powerful and hulking Nether dragons; mystical Ender dragons.

In the egg stage, dragons could live indefinitely in suspended animation. Were any dragon eggs to be discovered, they would still be viable even now. The hard egg shells and perfectly controlled internals kept the embryonic dragon safe and nurtured.
After hatching, the dragon's lifespan was no less impressive. The creatures lived for so long at a time that the humans and Other People wondered if they were functionally immortal -- never dying, but able to be killed. A century-old dragon could still be considered a youngling.

Dragons had all basic senses, and they also seemed to have a heightened sense of emotional auras. They were deeply spiritual beings and tripped the line between simply sentient and sapient. Most dragons relied on their sight and smell as their primary sensory inputs.

Despite their longevity, dragons were still very much mortal (otherwise they would not have gone extinct.) In the Overworld, they either could not cope with environmental changes post-Fall or were hunted to extinction in the ensuing Gold Age. The last of the Nether dragons died in radioactive devastation of the final Nether Wars. It is not known how the dragons in the End, save for the Ender-Dragon herself, went extinct.
As far as common knowledge goes, the Ender-Dragon is the last of her kind, and were she to die, her species would die with her. Even so, some have refused to give up hope. There is talk of surviving dragon eggs hidden in very remote places within the three dimensions. Perhaps some brave and kind explorer will, someday, find these eggs and rekindle this noble species's legacy.