Due to the weakening of boundaries that separate the various planes of existence, the Hylden's strength over the realm of Nosgoth is increasing. This allows them within various degrees the ability to possess hapless victims and subvert them to their cause. Usually this involves the invasion of the host by a transient disembodied Hylden soul. Once taken over the effects can be varied. The lightest possessions merely increase the strength and ferocity of the victim, while the heaviest can not only re-purpose the mind for their uses but the very skin and bone as well. In these heaviest of cases, the very body of the host is twisted and disfigured into monstrous size and deformity.
―Legacy of Kain: Defiance: Prima's Official Strategy Guide[Defiance strategy guide]