There are 493 Pokémon in Pokémon Brilliant Diamond and Shining Pearl and you will need all of them if you want to complete the Pokédex. One Pokémon you will need is Togepi and its evolutions, Togetic, and Togekiss. You might be wondering where to find Togepi in Pokémon Brilliant Diamond and Shining Pearl.
To find Togepi in Pokémon Brilliant Diamond and Shining Pearl, you can head to the Grand Underground or Route 230. Togepi can be found in Fountain Spring Cave, Stargleam Cavern, or Dazzling Cave in the Grand Underground. Route 230 also has Togepi, this location is accessed later in the game.
Togepi's final evolution, Togekiss, is a fantastic flying and fairy-type Pokémon. Its new fairy typing makes it great at taking out dragon-type Pokémon. Combine that with its flying-typing and it becomes a great Pokémon against Cynthia's Gachomp.
Togepi will evolve into Togetic when its friendship has reached a high enough level. To evolve Togetic into Togekiss, you will need to get your hands on a Shiny Stone. Regardless of if you intend to use Togekiss on your team, you will need this evolution line to complete your Pokédex.
For more information on Pokémon, check out All HM Locations in Pokémon Brilliant Diamond and Shining Pearl and How to get Tangrowth in Pokémon Brilliant Diamond and Shining Pearl on Pro Game Guides.