There are some parts of Pokémon Shining Diamond and Shining Pearl where you will struggle to progress in the game. For example, you might have trouble with one aspect of the game is getting through the Psyduck barricade next to the Coffee Cabin on Route 210. Here's what you need to know about how to get past those Psyducks and progress through the rest of Pokémon Brilliant Diamond and Brilliant Pearl.
You will only be able to do this by progressing in history. It will happen after beating Pastoria City Gym Leader Wake and earning the fourth Gym Medal. After that, you will have to face the force of Team Galaxy in the city and fight against them.
The next step is to wait for Cynthia to talk to your character. She will explain that the Psyduck blocking your path has a problem and she offers you an item, the secret medicine, that you can use to improve them and encourage them to move.
Now, with the secret medicine, all you have to do is go back to the Psyduck next to the coffee booth and interact with them. You will see an exclamation point above their head and they will disperse from position, allowing you to pass. This is all tied to history, so you won't be able to miss any of these elements as long as you play Pokémon Brilliant Diamond and Brilliant Pearl.
