Rune dragons are found in the remains of Mount Firewake, where the Kethsians kept the Stone of Jas, until it was overused and awakened the Dragonkin. Also located in this area is the laboratory of the DactylForcae, a disciple of Kerapac, who created the adamant and rune dragons.
If the player dies on Mount Firewake, their gravestone spawns near the World Gate.
Rune dragons have a total of three phases that must be completed with each kill, with the first phase requiring the use of dragonbane bolts or arrows in order to break through their metallic armour and with the second phase being unreachable with melee weapons.
As with mithril and adamant dragons, rune dragons use all three styles of combat, in addition to the standard dragonfire. Their magic and melee attacks are simply standard attacks, while their ranged attack will freeze the player for one second, which can be avoided with Freedom and Anticipation. During their second phase, their standard dragonfire is replaced with an "enhanced" dragonfire. The "enhanced" dragonfire is not as strong as it implies; rather, it functions similarly to the Queen Black Dragon's dragonfire, though it is avoidable.
Starts with 45,045 life points. Any attacks during the transition will be reduced to 10% damage. 
The dragon begins flying and becomes immune to melee attacks. Dragonbane is no longer required to deal full damage. In addition, the dragon stops using melee attacks and replaces its standard dragonfire attack with the enhanced version.
Throughout this phase, the rune dragon may breathe a bright blue plume of enhanced dragonfire, dealing magic damage. This attack cannot be fully blocked by a super anti-fire or wyrmfire potion, and will deal a minimum of 450 magic damage. However, if the player is far enough from the dragon, a small cloud appears under the player indicating the enhanced dragonfire is being used and can be avoided by moving away from it.
Upon release, there was a bug that caused Rune dragons to build up their rage outside of combat, due to players leaving combat during the third phase. This caused them to easily kill players in a single hit. This bug was patched the following day. Without growing their rage, rune dragons will still keep their rage for a long time after leaving combat. If one leaves for a bank trip, it is common to find their already damaged dragon in the same state as it was before leaving.
There is currently a glitch where damage from a dwarf multicannon deals full damage for phase one of the fight, even though dragonbane ammo is required in order to harm them.
On release, rune dragons were aggressive and had fewer spawns. With the Patch Notes update on 22 June 2015, several changes were implemented, such as increased experience, tolerance towards players, more spawns, and reduced damage from their enhanced dragonfire.
Originally, as a rune dragon had to reach a specific threshold of life points to move to the next phase, overhitting the mark would result in the dragon regenerating all lost health back to the specific health mark (e.g if the rune dragon had 46,000 life points and was hit by a Tuska's Wrath on a Slayer assignment, it would have 34,000 life points; the next hit would result in its health returning to the transition threshold of 45,050 life points). In addition, rune dragons could not be attacked during phase transition. This was changed on 22 August 2016 due to player complaints.
If a rune dragon is forced into its next phase via indirect damage, it will turn aggressive towards the player that caused the phase transition.
Rune dragons (and their elite variant) are the only metallic dragons to have no weaknesses.
^ abJagex. Patch Notes | 22/08. RuneScape Official Forums. 22 August 2016. "Made changes to rune dragons' phase transitions to allow players to continue attacking throughout. Damage that overshoots the lifepoint thresholds will no longer be healed back, but that hit, and hits during transition, are reduced to 10% power."*