Metallic Pokémon are one of the rare variant of Pokémon in Pokémon Vortex. Metallic Pokémon have 25% more defence than Normal Pokemon
They were made by staff of Pokemon Vortex. Hence they're not to be used on any sites other than pokemon-vortex.com and pokemonvortex.com. Example:
This Metallic Munchlax is a different colour. However, you cannot catch a Metallic evolved Pokémon, as all evolved Pokémon can only be caught in the Normal Variant. Metallic Legendary Pokémon, however, CAN be caught.