The Fusion Dragon is the combined form of Kai and Nya's Elemental Dragons.
The Fusion Dragon is a two-headed dragon created by the use of the Dragon Blade, which combines the powers of two elements together in a divergent process from that used to create the Water/Lightning Dragon in "Wishmasters". Kai and Nya's dragon unites their powers of Fire and Water, and is thus capable of surviving the hospitable environment of the Boiling Sea. It was previously formed by Ray and Maya to hide the last of the Time Blades in the library of Hono Mizu, and later by Kai and Nya to reach the library and escape from it when it began to collapse due to a booby trap. They would subsequently use it to travel back to the Vermillion swamp and then pursue the Iron Doom back in time, where they would use the dragon to battle the giant vehicle and later follow it back into the temporal vortex.
The Dragon performed best when controlled by both Kai and Nya, though one of them could fly it alone for a time if needed; the two also regarded the Fusion Dragon as a female.