The revenant dragon is a level 126 revenant. They are, however, much stronger than other monsters of a similar level. It is the only members-only revenant. Revenant dragons can hit moderately high very often with their accurate attacks, and have high defense despite having no weakness, so they will not go down as easily as other revenants.
Like all revenants, they can recover lost health (in intervals of 1,735), can cure themselves of poison and can quickly react to a player's protection prayers/curses.
Revenant dragons are the only revenants capable of poisoning the player. This poison damage only occurs through their ranged attacks.
Revenant dragons are less likely to be killed due to the fact other revenants are considerably easier to kill, as the dragon has very high defence, a large amount of hitpoints and can deal more damage. However, they do have the highest drop rate for all revenant related drops.
The Forinthry Dungeon is a PVP-enabled area, meaning it is entirely possible for other players to attack you while fighting the revenants in the dungeon. Do not bring equipment that you are not willing to lose.
Revenant dragons had two heads before the dragon graphical update on 5 July 2010.
It is very possible that they are the spirits of white dragons. On examination of the Third Age ranger armour, it says it is made of white dragonhide. These dragons would've then existed around the time of the God Wars, and have gone extinct/into hiding shortly after.
Prior to the Evolution of Combat, revenant dragons were the strongest revenants. After the update, their combat level was lowered for unknown reasons; however, a subsequent update returned them back to their original position.
Revenant dragons are not shown in Jagex's bestiary. This is most likely an oversight.