Dragon City: Battleground

The strongest dragon for me is pure dragon. It is said to be the hardest to breed. It requires 2 legendary/wind/crystal/mirror dragon. The chances are low but during that period, you probably will fill up your dragon book.

The main reason is simple. It have 3 pure moves. Pure fire, pure and pure metal moves. It doesn't possess any weakness to any moves nor advantage. The other move would be fire skill, lava balls. Lava balls damage is low but it won't be your main skill since pure damage (any one of the 3 skills) against neutral is highest in the game. With these 4 skills, fire possess advantage above ice and water dragon, pure fire above fire dragon, pure metal above metal dragon and against other elements just use pure metal moves since its animation time is short, saves your time fighting. Pure metal skill is weak against pure metal dragon and laval balls and pure fire skill is weak/immune against pure fire dragon. So, always beware of pure fire and pure metal dragon. Train them to level 30 and 3 stars and you will be totally invincible.