The Pokédex Professor Rowan gives you at the start of the game is the Sinnoh Pokédex. It contains data on all 150 Pokémon in the region (plus Manaphy), including starters like Chimchar, Piplup, and Turtwig. If you want to discover more than these 150, you need what is called a National Pokédex.
What Pokémon are included in the Brilliant Diamond and Shining Pearl National Pokédex
The National Pokédex for these two games contains all 493 Pokémon from the first four regions of the series (Kanto, Johto, Hoenn, and of course, Sinnoh). That's over 300 new Pokemon! Pokemon like Eevee and Charmander can only be encountered in the wild once you've unlocked the National Pokédex.
How to get the National Pokédex in Brilliant Diamond and Shining Pearl
Like any national Pokédex unlock, you must encounter (not capture) all 150 native Sinnoh Pokémon. This does not include #151 Manaphy, which you can give as a gift. Considering the long list of exclusive Pokémon in Brilliant Diamond and Shining Pearl, you need to trade a lot to complete the Sinnoh Pokédex.
Related: All Grand Underground Pokemon In Brilliant Diamond & Shining Pearl
Once you've seen all 150 Pokemon, talk to Professor Rowan in his lab in Sandgem Town. Professor Oak will come later and upgrade your device in the National Pokédex. Professor Rowan will also give you the Poké Radar, which allows you to chain Pokémon encounters. This will allow you to hunt shards more effectively.
For more help with Pokémon Brilliant Diamond and Shining Pearl, we at Tipsforallgames have you covered.
