I come from Ferelden, a country in southern Thedas. Revenants in Thedas are the result of extremely powerful demons (usually Pride demons) possessing corpses. They are generally armored, able to use some magic, immune to most magic and many physical assaults, extremely hostile, and have been known to take down entire units of trained soldiers. Still not as dangerous as a demon in its true form, however, and I will agree that successfully killing them is indeed fun.