Blizzard Dragon

Breeding
You can get this dragon by breeding a Water Dragon with a Fire Dragon at the Breeding Mountain or Ultra Breeding Tree.

Breeding a Water Dragon with a Fire Dragon may also result in a Cloud Dragon.

Damage Calculator
To explain, When attacking with Fire, Blizzard deals double damage against Water and Ice, half damage against Earth and Fire, and no damage against Metal. when attacking with Water, Blizzard deals double damage against Fire and Electric, medium damage against Water and Ice, and no damage against Plant. When defending, Blizzard takes double damage from Fire and Dark, medium damage from Water and Plant and take no damage from Earth.

Trivia

 * Although it is a Blizzard Dragon, since blizzard is Ice, and it keeps spitting snowflakes, its element is Water and Fire. It even looks like it's Ice.
 * Also breeding Cloud Dragon and Mud Dragon gives higher success than others. (tested by breeding 3 out of 5 tests results in blizzard dragon)