Hylden Revenants were a type of Revenant encountered in Defiance. Hylden Revenants were created by Hylden entering the Material Realm by Possession of Hylden corpses. The creation of these Revenants required Hylden corpses, hence they were mainly seen in Hylden areas like the Avernus Catacombs.
Hylden Revenants were the strongest of the 'resurrected' Revenants, caused by a resonance of a Hylden Soul with a Hylden body. Hylden Revenants could also fly into a 'Berserker Rage', during which time it would increase in strength and speed and wildly lash out at the player whilst it was virtually impervious to attack.
Legacy of Kain: Defiance - Prima Official Guide.