Leviathan is a shiny Gyarados that Emerald caught at the Lake of Rage in the Johto region. Gyarados was originally a Magikarp that was affected by the soundwaves made by Team Rocket as part of their plan. Leviathan is one of Emerald's most powerful Pokemon even after getting caught. Thanks to his Adamant nature and trained in attack power, speed, and enduring hits, he is capable of causing all sorts of destruction: Like changing the landscape with an Earthquake, or sweeping entire armies with a single Twister, etc.