Ultra Dragon

"... Just like us, they have reached their full potential."- Zane: Day of the Great Devourer

The Hydro-Dragon is a powerful combination of all the dragons when they have reached adulthood. The four dragons went to the Spirit Coves to grow up. They were combined into one large entity.

History
At first, the dragons were not heard of since Snakebit, however, they returned to fight and save the ninjas. Combining their power, they struck the Great Devourer down. However, the Great Devourer returned the fight and took them out of the air. They seemed to be alright after Lord Garmadon killed the Devourer once and for all.