There are a lot of items in Pokémon Brilliant Diamond and Shining Pearl. Some change the landscape of battles when held by Pokémon, while others provide new ways to catch Pokémon. We'll show you how to get the key item, the old rod, and the held item, quick claw, in your playthrough. There is only one requirement before you can claim one of the items.
After getting the Pokétch, head west to Jubilife City, you will see a small building, enter it and talk to the fisherman inside. Answer "yes" to his comments and he'll give you the Old Rod. The Old Rod can be registered on the plus button and has a one hundred percent chance of hooking a Magikarp. Pure water-type Magikarp only learns Splash and Action before evolving into the mighty Gyarados at level 20.
Head north of the Pokémart to the apartment building. Chat to the blonde woman inside with Pikachu and Pachirisu. He will give you the Fast Claw and explain how it works. When held by a battling Pokémon, they can sometimes attack first, even if their Speed stat is lower than that of their opponents. Some strong Quick Claw users at first are Geodude, Shinx, Bidoof, and Kricketot.