The National Dex. As Many people know allows you to get data on Pokémon not indigenous to the region. Well in this game its no different

Unlike Ruby/Sapphire However, Professor Birch gives you the National Dex right after you beat the Elite Four. The dex is vital as in the Battle Frontier and the other new areas, there will be trainers and Pokemon that are not seen in Hoenn Normally

 
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