Mirror Dragon

Fuck
You can get a Legendary Dragon by breeding two Rare Hybrid dragons with each other at the Breeding Mountain or Ultra Breeding Tree. These are: Star Dragon + Armadillo(28Hours) armadilo + cool fire
 * Cool-Fire Dragon
 * Soccer Dragon
 * Armadillo Dragon of time used) to use are:

Fossil Dragon + Penguin Dragon (28 Hours)

You can also get the Mirror Dragon with 7 Guesses (20-24 September, 2016, or 10 Guesses (30 September - 10 October, 2016) in Carnival Games.

Damage Calculator
To explain, when attacking with Legendary, Mirror deals double damage against other Legendary Dragons, and normal damage against everything else (?). When defending, Mirror takes double damage from Legendary Attacks and half damage from Physical Attacks.