Yliaster is an alchemical term that refers to the prima materia, the base component of the philosopher's stone. It is the base material from which all matter derives.
Design
Yliaster appears as a giant multi-headed snake. This appearance may be related to another name for the prima materia, "The Serpent" or "The Dragon", which appears in Martin Rulandt's Lexicon alchemiae, a dictionary of alchemical terms.