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.
Unlike other revenants, revenant dragons are poisonous.
Revenant dragons are less likely to be killed due to the fact other revenants are much weaker, the revenant dragon is poisonous, and the revenant dragon spawn is a PKer hotspot. However, revenant dragons are more likely to drop Ancient Warriors' equipment more often than its other revenant counterparts.
WARNING: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 graphics 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.
Revenant dragons used to have low defence for a while after the Evolution of Combat. After a hidden update, their defence level has increased dramatically, even more than a revenant knight.
Revenant dragons are not shown in Jagex's bestiary. This is most likely an oversight.