Revenant physical attack has a chance of inflicting Poison on hit, but otherwise are not much of a threat to a properly trained party. Since Revenants are undead, items like Potions or Cure-type spells and Holy does damage, are susceptible to the Fire tier of Black Magic, and are defeated easily with Raise or Phoenix Down. Any absorption attacks will backfire and the user will lose HP. Furthermore, Revenants are immune to Toad and Confusion.
Revenants are animated corpses or ghosts in Western folklore that are said to return from the dead to terrorize the living. The word "revenant" is French (Fr. revenir, "to return") and means "one who returns".