Dragons

The Elemental Dragons are mystical creatures that belong to both Ninjago and The Underworld, and ferry between them. They are the guardians of the four Golden Weapons and are generally not vicious unless the weapon is threatened.

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..

History
The four ninjas Wu selected 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 wanted only to protect the weapons, and would gladly aid the ninjas in their quest. Each ninja now keeps the dragon matching their elemental properties as a pet, in addition to using it for transportation. This allows the dragons to continue guarding the weapons, as the four ninjas now wield them in defense of Ninjago. When Jay deciedes to visit his parents, their dragons shed their scales and have to leave the ninjas while they have to go on a long journey to where Jay was born: a junkyard known as "Ed & Edna's Scrap & Junk."