Kinds of Dragons
Ninjago has four known Dragons: The Fire Dragon, the Lightning Dragon, the Ice Dragon, and the Earth Dragon. Sensei Wu placed each Dragon to guard one of the Golden Weapons, each in tune with its elemental properties.
The four Ninja had to avoid each of the Dragons as they recovered the four Golden Weapons. When the Weapons were stolen by Garmadon, they discovered that the Dragons only wanted to protect the Weapons, and would gladly aid the Ninja in their quest. Afterwards each Ninja kept the Dragon matching their elemental properties as a pet, in addition to using them for transportation. This allowed the Dragons to continue guarding the Weapons, as the four Ninja wielded them in defense of Ninjago. As Jay decided to visit his parents, all four Dragons were molting and had to leave the Ninja. The Ninja had to go on the journey to Ed & Edna's Scrap N Junk alone.
After their respective time away from the Ninja, the Dragons morphed into the Ultra Dragon. It appeared during the fight against the Great Devourer and nearly defeated the creature. It is now Lloyd's form of transportation. He used in it in Ninjaball Run.