Below is an extract from the games files
it shows all the Breedable Legendary dragons that also have a status of breedable.
This page updates automatically when the game files update
Apocalypse Dragon
Millennium Dragon
Forge Dragon
Promethium Dragon
Abyss Dragon
Mirage Dragon
Supersonic Dragon
Decay Dragon
Quasar Dragon
Shapeshifter Dragon
Morpheus Dragon
Animowl Dragon
There are 3 methods that will work for breeding legendary dragons, The first (most common) tactic is to breed a Pure Dragon with a War Dragon.
This has a 40% chance of breeding the Kratus Dragon who knows both Pure and War type moves.
Because the breed rate is so high, it is reccomended to do this reptitively and recall the duplicate Kratus dragons using the tree of life.
The next option is to try and breed one of the many legendary dragons that have a single element of Legend.
This can be done by breeding 2 Pure dragons together, and is estimated to have a 1% success rate.
It can take a long time, and one of the only ways to get the "Legacy Dragon" which is needed for a perticular quest later in the game.
The other way is to upgrade your breeding santuary, which unlocks new breeding possibilities but only when breeding on the sanctuary itself.
There are a number of legendary dragons available from later stages of the breeding sanctuary