Dragons are creatures with nearly unlimited life spans. They can survive for long periods of time, and no one has found a dragon that has died of old age. Adolescence is usually marked by the growth of a hatchling's wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. Once they hit adolescence, hatchlings change quickly, maturing to their full forms in only 2 years.

Dragons don't communicate with each other verbally, but they will growl to scare off predators and frighten prey. Young dragons will emit an extremely high-pitched squeal when they are frightened. To communicate, they use telepathy with each other and to speak to other creatures.

Green dragons are also sometimes called "earth" dragons. They usually live deep within caves, and have power over the earth. They are capable of launching boulders at high speeds, and can cause earthquakes by slamming down onto the ground.

Diseased, along with his twin sister, Sickly, were the second generation of neglected dragon research. Born from Sickness, the first to be entered in the neglected experiment, and her father Takashi Okami, the researcher assigned to the experiment decided to try to exploit family lines it see if they could get a result. Both children grew up to be normal dragons; although they are weak and have many health problems from the neglect. A third egg was laid but the researcher was either careless or showed some compassion for these dragons... either way it ended up in the abandoned pile where someone found it and raised it to be a happy and healthy fully-grown dragon.