Some people take longer to fully express their potential than others. In addition to training attributes and practicing new spells and skills, it is possible for some races to evolve into more advanced creatures during their leveling progress. Such evolution is accomplished with the rebuild command and is voluntary. After a successful rebuild you may find you're better than you were before: better - stronger - faster!
In particular, the firedrake race is known to evolve from a hatchling of moderate destructive potential into a fearsome beast. Likewise, the cute little fuzz balls called "verbits" are capable of becoming huge, fierce, deadly balls of fuzz. On account of this evolution, it is advised not to keep verbits as pets.
These races are currently not available for creation.