Diethons are serpentine monsters as large as grown men with vivid purple scales, their most notable feature being the pair of yellow wing-like membranes on their sides. They also have orange spots and yellow spines running down the length of their bodies. The serpents are very venomous, able to poison opponents by biting with their sharp fangs or exhaling a noxious mist. They can also utilise their powerful tails in slamming or swiping attacks.
In the Wayfarer's Pass cave, a Hacksaurus (later named Lizzie) is seen guarding her eggs that hatch into Diethons when interacted with. While the two monsters are completely different in terms of appearance and abilities, it may suggest that there is a metamorphic relationship between the two types of monster. In later games such as IX and XI, diethons have been made part of the Dragon family like many other reptilian monsters.
These sickening snakes are immune to poison, can vomit up a Venom Mist, and will run at the sight of superior strength. Superstition says to take three steps back and set off somewhere else if a diethon crosses your path at night.