The revenant pyrefiend is a type of revenant that inhabits the Revenant Caves, which is a PvP-enabled area that is part of the Wilderness. It is entirely possible for other players to attack you whilst fighting the revenants in the dungeon. Do not bring equipment that you are not willing to lose! Like all revenants, they are susceptible to the effects of the Salve amulet, can restore health when it falls below 50% and react quickly to a player's protection prayers.