Each Fever Wyvern carries a unique and very deadly disease on the spines of its tail. To make up for a lack of physical strength, the dragons use this disease to their advantage by poisoning prey and fending off attackers. The illness will quickly render victims helpless before eventually killing them. A Fever will track its prey until the target can no longer move. Usually a solitary breed, these dragons will only come together during mating season, and will flare out the brightly colored sails along their wings to help attract potential mates. Although it has been observed that the wyverns are nocturnal, they will often pick an open spot of sunshine to curl up in and sleep as the day passes by.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons 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. In Galsreim, dragons and humans coexist peacefully.

The form of disease that Basil carries is peculiar, to say the least. It imbues those affected with an exaggerated sense of bravado while also greatly decreasing their muscular strength, causing them to charge into dangerous situations without a second thought, usually to their doom. This allows Basil to gather the scraps without having to do any of the dirty work, except for when the victim decides to charge at Basil. He is somewhat of an outcast among the dragons hatched at Damian's oasis due to the potency of his disease, usually taking to the desert.