Board Thread:Dragon City Gameplay Questions & Answers/@comment-10799351-20130812143126/@comment-14284922-20130812162602

Leviathan Dragon is a rare hybrid. You would need to mix a war hybrid with a water hybrid to breed it.

One example: Colossal Dragon + Mud Dragon.

This could result in:

Terra, Mud, Waterfall, Colossal or Leviathan.