From Bulbapedia, the community-driven Pokémon encyclopedia.
This is a list of Pokémon that do not appear in any Regional Pokédex, ordered according to the National Pokédex. So far, all of the Pokémon that fit this description are legendary
This includes Generation IV Pokémon that do not appear in the extended Sinnoh Pokédex.
List of Pokémon that do not appear in any regional Pokédex