Dragons

The Dragons are mystical creatures that originated from the Realm of Oni and Dragons. They are said to be connected to both Ninjago and the Underworld, enabling them to travel between the two worlds at will. They were the Guardians of the four Golden Weapons, and were generally not vicious unless the Weapons are threatened.

The Original Dragon

 * The Firstbourne Dragon (The mother of all Dragons)

Types of Dragons
There are ten known types of Dragons:
 * Fire Dragon
 * Lightning Dragon
 * Ice Dragon
 * Earth Dragon
 * Ultra Dragon
 * Nindroid MechDragon
 * Light Dragon
 * Shadow Dragon
 * YinYang Dragon
 * Ghost Dragons

Known Hybrid Dragons

 * First Spinjitzu Master (of Oni descent)
 * Garmadon (of Oni and human descent)
 * Lloyd (of Oni and human descent)
 * Wu (of Oni and human descent)

History
The Dragons seen in Ninjago were descended from the Dragons of the Realm of Oni and Dragons. These original Dragons had the power of Creation, and constantly waged war against their arch enemies, the Oni (who were beings of Destruction, the polar opposite of Creation).

Master Wu placed each Dragon to guard one of the Golden Weapons, each in tune with its elemental properties. The dragons guarded the weapons for many years, until an increase in Skulkin activity led Master Wu to believe that the weapons had to be retrieved before they could fall into Lord Garmadon's hands.

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 on foot.

During their time in the Spirit Coves, the Dragons morphed into the Ultra Dragon. It appeared during the fight against the the Great Devourer and nearly defeated the creature. It briefly served as Lloyd's personal transportation until he mastered the Golden Dragon, most notably in "Ninjaball Run."

When the Overlord possessed Garmadon's body in "Return of the Overlord," he appeared as a humanoid dragon. As his power continued to increase in the following episode, he mutated into a full dragon.