There are numerous Pokémon that you can encounter in Pokémon Brilliant Diamond and Shining Pearl. These Pokémon are elusive, but some of them have specific requirements that you must meet to find them. For example, Poliwhirl can evolve into Politoed and you need an item to do that. In this guide, we will detail how you can evolve Poliwhirl into Politoed in Pokémon Brilliant Diamond and Brilliant Pearl.
The only way to evolve Poliwhirl is to find a King's Rock. The King's Rock is an exclusive evolution item and can be found by catching a Pokémon. You can find it on Poliwhirl by catching it in the wild. Poliwhirl spawns when you unlock the National PokéDex, which means you'll need to finish the game and complete your Sinnoh PokéDex to find it. You mostly want to find it while searching the Grand Underground. You can find it everywhere, and Poliwag.
When you catch a Poliwhirl with King's Rock, the next step is to place it on the Poliwhirl you want to evolve into Politoed and trade it with a friend. When Poliwhirl trades while carrying this item, it automatically becomes Politoed. Your friend will then have to exchange it with you, and then you will receive Politoed.