Name Any animal that Pokemon never did.

[TomGuycott]

The Leviethan and The World's Serpent as rival legendaries.

Kyogre and Groudon are meant to be considered Pokemon's Leviathan and Behemoth equivalents. There was also a third one Ziz, an air related one whereas the Behemoth was earth and the Leviathan was sea. However, Ziz is more of a gryphon thing.

To be honest, Rayquaza does kind of fit the bill of a World Serpent-like legendary, though.