The Spooky Plate is an item that boosts the damage of Ghost-type attacks in Pokemon Brilliant Diamond and Shining Pearl.
It is a held item that can be given to a Pokemon. From there, any Ghost-type attack they use will deal extra damage. This can be dangerous when given to a Ghost-type creature, especially when considering the Same Type Attack Bonus, too.
If dishing out insanely powerful Ghost-type attacks in Pokemon Brilliant Diamond and Shining Pearl is your plan, then you need to head to Hearthome City. That is where you will find the Spooky Plate.
Where to find the Spooky Plate in Pokemon Brilliant Diamond and Shining Pearl
Hearthome City can be accessed after defeating the Eterna City Gym Leader. Exit Eterna City to the south on Route 206. Follow the path to the east on Route 207 and Route 208 after.
This will bring you to Hearthome City in Pokemon Brilliant Diamond and Shining Pearl. Go to the northern part of the city and find the top right corner. There is a small building behind the Gym.
Go through this building and a receptionist will stop you. Agree to enter with a cute Pokemon and you will be inside of Hearthome City's Amity Square. Walk with your partner all the way to top of the park.
Move to the far right corner and you will come across two stone structures that resemble houses. You can go inside of this, but you won't load into the interior like other buildings.
By the house on the right side, there is a Poke Ball on the ground that you can interact with and pick up. Press A on it and you will grab the Spooky Plate and add it to your inventory.
Now, you can give that to a Ghost-type in Pokemon Brilliant Diamond and Shining Pearl to make them even more powerful. Also, if it is your first time in Amity Square, leave to gain the ability to walk with your partners throughout Sinnoh.