Regional Pokédex/Non-native Pokémon

From Generation III onward, Pokémon not native to a region which are obtained (such as through trading) before a game's regional Pokédex has been upgraded to National Mode will be displayed with ??? as their Pokédex number in the status screen instead of a regional Pokédex number. If caught from the wild (through hacking the game), the Pokédex registration screen will display different numbers dependent on the game: Ruby, Sapphire, and Emerald display a number between 203 and 386, corresponding to the Pokémon's position in the National Pokédex minus those Generation I and Generation II Pokémon native to Hoenn (for example, is the first Pokémon not in the Hoenn Pokédex so its number appears as #203, while  is #226, but Pikachu, Raichu, Sandshrew, and Sandslash appear in the Hoenn Pokédex and are skipped, making  #227). Pokémon FireRed and LeafGreen state only that the Pokémon's data has been registered, then skip straight to nicknaming the Pokémon, never displaying the Pokédex.

Generation IV games instead display the registered Pokémon as #000 if it is outside of that game's regional Pokédex.

Pokémon Omega Ruby and Alpha Sapphire will display an empty Pokédex entry upon catching a non-native Pokémon.

In Generation VII games, due to the lack of a National Pokédex, non-native Pokémon that are caught will completely bypass the Pokédex, skipping straight to nicknaming; these Pokémon have no Pokédex numbers.